diff --git a/build-aux/hydra/gnu-system.scm b/build-aux/hydra/gnu-system.scm
index d6b0132807..150c2bdf4f 100644
--- a/build-aux/hydra/gnu-system.scm
+++ b/build-aux/hydra/gnu-system.scm
@@ -50,409 +50,12 @@
                      dir)
              (set! %load-path (cons dir %load-path))))))
 
-(use-modules (guix config)
-             (guix store)
-             (guix grafts)
-             (guix profiles)
-             (guix packages)
-             (guix derivations)
-             (guix monads)
-             (guix ui)
-             ((guix licenses) #:select (gpl3+))
-             ((guix utils) #:select (%current-system))
-             ((guix scripts system) #:select (read-operating-system))
-             ((guix scripts pack)
-              #:select (lookup-compressor self-contained-tarball))
-             (gnu bootloader)
-             (gnu bootloader u-boot)
-             (gnu packages)
-             (gnu packages gcc)
-             (gnu packages base)
-             (gnu packages gawk)
-             (gnu packages guile)
-             (gnu packages gettext)
-             (gnu packages compression)
-             (gnu packages multiprecision)
-             (gnu packages make-bootstrap)
-             (gnu packages package-management)
-             (gnu system)
-             (gnu system vm)
-             (gnu system install)
-             (gnu tests)
-             (srfi srfi-1)
-             (srfi srfi-26)
-             (ice-9 match))
+(use-modules (gnu ci))
 
 ;; XXX: Debugging hack: since `hydra-eval-guile-jobs' redirects the output
 ;; port to the bit bucket, let us write to the error port instead.
 (setvbuf (current-error-port) _IOLBF)
 (set-current-output-port (current-error-port))
 
-(define* (package->alist store package system
-                         #:optional (package-derivation package-derivation))
-  "Convert PACKAGE to an alist suitable for Hydra."
-  (parameterize ((%graft? #f))
-    `((derivation . ,(derivation-file-name
-                      (package-derivation store package system
-                                          #:graft? #f)))
-      (description . ,(package-synopsis package))
-      (long-description . ,(package-description package))
-      (license . ,(package-license package))
-      (home-page . ,(package-home-page package))
-      (maintainers . ("bug-guix@gnu.org"))
-      (max-silent-time . ,(or (assoc-ref (package-properties package)
-                                         'max-silent-time)
-                              3600))              ;1 hour by default
-      (timeout . ,(or (assoc-ref (package-properties package) 'timeout)
-                      72000)))))                  ;20 hours by default
-
-(define (package-job store job-name package system)
-  "Return a job called JOB-NAME that builds PACKAGE on SYSTEM."
-  (let ((job-name (symbol-append job-name (string->symbol ".")
-                                 (string->symbol system))))
-    `(,job-name . ,(cut package->alist store package system))))
-
-(define (package-cross-job store job-name package target system)
-  "Return a job called TARGET.JOB-NAME that cross-builds PACKAGE for TARGET on
-SYSTEM."
-  `(,(symbol-append (string->symbol target) (string->symbol ".") job-name
-                    (string->symbol ".") (string->symbol system)) .
-    ,(cute package->alist store package system
-           (lambda* (store package system #:key graft?)
-             (package-cross-derivation store package target system
-                                       #:graft? graft?)))))
-
-(define %core-packages
-  ;; Note: Don't put the '-final' package variants because (1) that's
-  ;; implicit, and (2) they cannot be cross-built (due to the explicit input
-  ;; chain.)
-  (list gcc-4.8 gcc-4.9 gcc-5 glibc binutils
-        gmp mpfr mpc coreutils findutils diffutils patch sed grep
-        gawk gnu-gettext hello guile-2.0 guile-2.2 zlib gzip xz
-        %bootstrap-binaries-tarball
-        %binutils-bootstrap-tarball
-        (%glibc-bootstrap-tarball)
-        %gcc-bootstrap-tarball
-        %guile-bootstrap-tarball
-        %bootstrap-tarballs))
-
-(define %packages-to-cross-build
-  %core-packages)
-
-(define %cross-targets
-  '("mips64el-linux-gnu"
-    "mips64el-linux-gnuabi64"
-    "arm-linux-gnueabihf"
-    "aarch64-linux-gnu"
-    "powerpc-linux-gnu"
-    "i586-pc-gnu"                                 ;aka. GNU/Hurd
-    "i686-w64-mingw32"))
-
-(define %guixsd-supported-systems
-  '("x86_64-linux" "i686-linux" "armhf-linux"))
-
-(define %u-boot-systems
-  '("armhf-linux"))
-
-(define (qemu-jobs store system)
-  "Return a list of jobs that build QEMU images for SYSTEM."
-  (define (->alist drv)
-    `((derivation . ,(derivation-file-name drv))
-      (description . "Stand-alone QEMU image of the GNU system")
-      (long-description . "This is a demo stand-alone QEMU image of the GNU
-system.")
-      (license . ,gpl3+)
-      (home-page . ,%guix-home-page-url)
-      (maintainers . ("bug-guix@gnu.org"))))
-
-  (define (->job name drv)
-    (let ((name (symbol-append name (string->symbol ".")
-                               (string->symbol system))))
-      `(,name . ,(lambda ()
-                   (parameterize ((%graft? #f))
-                     (->alist drv))))))
-
-  (define MiB
-    (expt 2 20))
-
-  (if (member system %guixsd-supported-systems)
-      (if (member system %u-boot-systems)
-          (list (->job 'flash-image
-                       (run-with-store store
-                         (mbegin %store-monad
-                           (set-guile-for-build (default-guile))
-                           (system-disk-image
-                            (operating-system (inherit installation-os)
-                             (bootloader (bootloader-configuration
-                                          (bootloader u-boot-bootloader)
-                                          (target #f))))
-                            #:disk-image-size
-                            (* 1024 MiB))))))
-          (list (->job 'usb-image
-                       (run-with-store store
-                         (mbegin %store-monad
-                           (set-guile-for-build (default-guile))
-                           (system-disk-image installation-os
-                                              #:disk-image-size
-                                              (* 1024 MiB)))))
-                (->job 'iso9660-image
-                       (run-with-store store
-                         (mbegin %store-monad
-                           (set-guile-for-build (default-guile))
-                           (system-disk-image installation-os
-                                              #:file-system-type
-                                              "iso9660"))))))
-      '()))
-
-(define (system-test-jobs store system)
-  "Return a list of jobs for the system tests."
-  (define (test->thunk test)
-    (lambda ()
-      (define drv
-        (run-with-store store
-          (mbegin %store-monad
-            (set-current-system system)
-            (set-grafting #f)
-            (set-guile-for-build (default-guile))
-            (system-test-value test))))
-
-      `((derivation . ,(derivation-file-name drv))
-        (description . ,(format #f "GuixSD '~a' system test"
-                                (system-test-name test)))
-        (long-description . ,(system-test-description test))
-        (license . ,gpl3+)
-        (home-page . ,%guix-home-page-url)
-        (maintainers . ("bug-guix@gnu.org")))))
-
-  (define (->job test)
-    (let ((name (string->symbol
-                 (string-append "test." (system-test-name test)
-                                "." system))))
-      (cons name (test->thunk test))))
-
-  (if (member system %guixsd-supported-systems)
-      (map ->job (all-system-tests))
-      '()))
-
-(define (tarball-jobs store system)
-  "Return Hydra jobs to build the self-contained Guix binary tarball."
-  (define (->alist drv)
-    `((derivation . ,(derivation-file-name drv))
-      (description . "Stand-alone binary Guix tarball")
-      (long-description . "This is a tarball containing binaries of Guix and
-all its dependencies, and ready to be installed on non-GuixSD distributions.")
-      (license . ,gpl3+)
-      (home-page . ,%guix-home-page-url)
-      (maintainers . ("bug-guix@gnu.org"))))
-
-  (define (->job name drv)
-    (let ((name (symbol-append name (string->symbol ".")
-                               (string->symbol system))))
-      `(,name . ,(lambda ()
-                   (parameterize ((%graft? #f))
-                     (->alist drv))))))
-
-  ;; XXX: Add a job for the stable Guix?
-  (list (->job 'binary-tarball
-               (run-with-store store
-                 (mbegin %store-monad
-                   (set-guile-for-build (default-guile))
-                   (>>= (profile-derivation (packages->manifest (list guix)))
-                        (lambda (profile)
-                          (self-contained-tarball "guix-binary" profile
-                                                  #:localstatedir? #t
-                                                  #:compressor
-                                                  (lookup-compressor "xz")))))
-                 #:system system))))
-
-(define job-name
-  ;; Return the name of a package's job.
-  (compose string->symbol
-           (cut package-full-name <> "-")))
-
-(define package->job
-  (let ((base-packages
-         (delete-duplicates
-          (append-map (match-lambda
-                       ((_ package _ ...)
-                        (match (package-transitive-inputs package)
-                          (((_ inputs _ ...) ...)
-                           inputs))))
-                      (%final-inputs)))))
-    (lambda (store package system)
-      "Return a job for PACKAGE on SYSTEM, or #f if this combination is not
-valid."
-      (cond ((member package base-packages)
-             (package-job store (symbol-append 'base. (job-name package))
-                          package system))
-            ((supported-package? package system)
-             (let ((drv (package-derivation store package system
-                                            #:graft? #f)))
-               (and (substitutable-derivation? drv)
-                    (package-job store (job-name package)
-                                 package system))))
-            (else
-             #f)))))
-
-(define (all-packages)
-  "Return the list of packages to build."
-  (define (adjust package result)
-    (cond ((package-replacement package)
-           (cons* package                         ;build both
-                  (package-replacement package)
-                  result))
-          ((package-superseded package)
-           result)                                ;don't build it
-          (else
-           (cons package result))))
-
-  (fold-packages adjust
-                 (fold adjust '()                 ;include base packages
-                       (match (%final-inputs)
-                         (((labels packages _ ...) ...)
-                          packages)))
-                 #:select? (const #t)))           ;include hidden packages
-
-(define (arguments->manifests arguments)
-  "Return the list of manifests extracted from ARGUMENTS."
-  (map (match-lambda
-         ((input-name . relative-path)
-          (let* ((checkout (assq-ref arguments (string->symbol input-name)))
-                 (base (assq-ref checkout 'file-name)))
-            (in-vicinity base relative-path))))
-       (assq-ref arguments 'manifests)))
-
-(define (manifests->packages store manifests)
-  "Return the list of packages found in MANIFESTS."
-  (define (load-manifest manifest)
-    (save-module-excursion
-     (lambda ()
-       (set-current-module (make-user-module '((guix profiles) (gnu))))
-       (primitive-load manifest))))
-
-  (delete-duplicates!
-   (map manifest-entry-item
-        (append-map (compose manifest-entries
-                             load-manifest)
-                    manifests))))
-
-
-;;;
-;;; Hydra entry point.
-;;;
-
-(define (hydra-jobs store arguments)
-  "Return Hydra jobs."
-  (define subset
-    (match (assoc-ref arguments 'subset)
-      ("core" 'core)                              ; only build core packages
-      ("hello" 'hello)                            ; only build hello
-      (((? string?) (? string?) ...) 'list)       ; only build selected list of packages
-      ("manifests" 'manifests)                    ; only build packages in the list of manifests
-      (_ 'all)))                                  ; build everything
-
-  (define systems
-    (match (assoc-ref arguments 'systems)
-      (#f              %hydra-supported-systems)
-      ((lst ...)       lst)
-      ((? string? str) (call-with-input-string str read))))
-
-  (define (cross-jobs system)
-    (define (from-32-to-64? target)
-      ;; Return true if SYSTEM is 32-bit and TARGET is 64-bit.  This hack
-      ;; prevents known-to-fail cross-builds from i686-linux or armhf-linux to
-      ;; mips64el-linux-gnuabi64.
-      (and (or (string-prefix? "i686-" system)
-               (string-prefix? "i586-" system)
-               (string-prefix? "armhf-" system))
-           (string-contains target "64")))    ;x86_64, mips64el, aarch64, etc.
-
-    (define (same? target)
-      ;; Return true if SYSTEM and TARGET are the same thing.  This is so we
-      ;; don't try to cross-compile to 'mips64el-linux-gnu' from
-      ;; 'mips64el-linux'.
-      (or (string-contains target system)
-          (and (string-prefix? "armhf" system)    ;armhf-linux
-               (string-prefix? "arm" target))))   ;arm-linux-gnueabihf
-
-    (define (pointless? target)
-      ;; Return #t if it makes no sense to cross-build to TARGET from SYSTEM.
-      (match system
-        ((or "x86_64-linux" "i686-linux")
-         (if (string-contains target "mingw")
-             (not (string=? "x86_64-linux" system))
-             #f))
-        (_
-         ;; Don't try to cross-compile from non-Intel platforms: this isn't
-         ;; very useful and these are often brittle configurations.
-         #t)))
-
-    (define (either proc1 proc2 proc3)
-      (lambda (x)
-        (or (proc1 x) (proc2 x) (proc3 x))))
-
-    (append-map (lambda (target)
-                  (map (lambda (package)
-                         (package-cross-job store (job-name package)
-                                            package target system))
-                       %packages-to-cross-build))
-                (remove (either from-32-to-64? same? pointless?)
-                        %cross-targets)))
-
-  ;; Turn off grafts.  Grafting is meant to happen on the user's machines.
-  (parameterize ((%graft? #f))
-    ;; Return one job for each package, except bootstrap packages.
-    (append-map (lambda (system)
-                  (format (current-error-port)
-                          "evaluating for '~a' (heap size: ~a MiB)...~%"
-                          system
-                          (round
-                           (/ (assoc-ref (gc-stats) 'heap-size)
-                              (expt 2. 20))))
-                  (invalidate-derivation-caches!)
-                  (case subset
-                    ((all)
-                     ;; Build everything, including replacements.
-                     (let ((all (all-packages))
-                           (job (lambda (package)
-                                  (package->job store package
-                                                system))))
-                       (append (filter-map job all)
-                               (qemu-jobs store system)
-                               (system-test-jobs store system)
-                               (tarball-jobs store system)
-                               (cross-jobs system))))
-                    ((core)
-                     ;; Build core packages only.
-                     (append (map (lambda (package)
-                                    (package-job store (job-name package)
-                                                 package system))
-                                  %core-packages)
-                             (cross-jobs system)))
-                    ((hello)
-                     ;; Build hello package only.
-                     (if (string=? system (%current-system))
-                         (let ((hello (specification->package "hello")))
-                           (list (package-job store (job-name hello) hello system)))
-                         '()))
-                    ((list)
-                     ;; Build selected list of packages only.
-                     (if (string=? system (%current-system))
-                         (let* ((names (assoc-ref arguments 'subset))
-                                (packages (map specification->package names)))
-                           (map (lambda (package)
-                                    (package-job store (job-name package)
-                                                 package system))
-                                  packages))
-                         '()))
-                    ((manifests)
-                     ;; Build packages in the list of manifests.
-                     (let* ((manifests (arguments->manifests arguments))
-                            (packages (manifests->packages store manifests)))
-                       (map (lambda (package)
-                              (package-job store (job-name package)
-                                           package system))
-                            packages)))
-                    (else
-                     (error "unknown subset" subset))))
-                systems)))
+;; Return the procedure from (gnu ci).
+hydra-jobs
diff --git a/gnu/ci.scm b/gnu/ci.scm
new file mode 100644
index 0000000000..8ece08e453
--- /dev/null
+++ b/gnu/ci.scm
@@ -0,0 +1,430 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2017 Jan Nieuwenhuizen <janneke@gnu.org>
+;;; Copyright © 2018 Clément Lassieur <clement@lassieur.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu ci)
+  #:use-module (guix config)
+  #:use-module (guix store)
+  #:use-module (guix grafts)
+  #:use-module (guix profiles)
+  #:use-module (guix packages)
+  #:use-module (guix derivations)
+  #:use-module (guix monads)
+  #:use-module (guix ui)
+  #:use-module ((guix licenses) #:select (gpl3+))
+  #:use-module ((guix utils) #:select (%current-system))
+  #:use-module ((guix scripts system) #:select (read-operating-system))
+  #:use-module ((guix scripts pack)
+                #:select (lookup-compressor self-contained-tarball))
+  #:use-module (gnu bootloader)
+  #:use-module (gnu bootloader u-boot)
+  #:use-module (gnu packages)
+  #:use-module (gnu packages gcc)
+  #:use-module (gnu packages base)
+  #:use-module (gnu packages gawk)
+  #:use-module (gnu packages guile)
+  #:use-module (gnu packages gettext)
+  #:use-module (gnu packages compression)
+  #:use-module (gnu packages multiprecision)
+  #:use-module (gnu packages make-bootstrap)
+  #:use-module (gnu packages package-management)
+  #:use-module (gnu system)
+  #:use-module (gnu system vm)
+  #:use-module (gnu system install)
+  #:use-module (gnu tests)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (ice-9 match)
+  #:export (hydra-jobs))
+
+;;; Commentary:
+;;;
+;;; This file defines build jobs for the Hydra and Cuirass continuation
+;;; integration tools.
+;;;
+;;; Code:
+
+(define* (package->alist store package system
+                         #:optional (package-derivation package-derivation))
+  "Convert PACKAGE to an alist suitable for Hydra."
+  (parameterize ((%graft? #f))
+    `((derivation . ,(derivation-file-name
+                      (package-derivation store package system
+                                          #:graft? #f)))
+      (description . ,(package-synopsis package))
+      (long-description . ,(package-description package))
+      (license . ,(package-license package))
+      (home-page . ,(package-home-page package))
+      (maintainers . ("bug-guix@gnu.org"))
+      (max-silent-time . ,(or (assoc-ref (package-properties package)
+                                         'max-silent-time)
+                              3600))              ;1 hour by default
+      (timeout . ,(or (assoc-ref (package-properties package) 'timeout)
+                      72000)))))                  ;20 hours by default
+
+(define (package-job store job-name package system)
+  "Return a job called JOB-NAME that builds PACKAGE on SYSTEM."
+  (let ((job-name (symbol-append job-name (string->symbol ".")
+                                 (string->symbol system))))
+    `(,job-name . ,(cut package->alist store package system))))
+
+(define (package-cross-job store job-name package target system)
+  "Return a job called TARGET.JOB-NAME that cross-builds PACKAGE for TARGET on
+SYSTEM."
+  `(,(symbol-append (string->symbol target) (string->symbol ".") job-name
+                    (string->symbol ".") (string->symbol system)) .
+    ,(cute package->alist store package system
+           (lambda* (store package system #:key graft?)
+             (package-cross-derivation store package target system
+                                       #:graft? graft?)))))
+
+(define %core-packages
+  ;; Note: Don't put the '-final' package variants because (1) that's
+  ;; implicit, and (2) they cannot be cross-built (due to the explicit input
+  ;; chain.)
+  (list gcc-4.8 gcc-4.9 gcc-5 glibc binutils
+        gmp mpfr mpc coreutils findutils diffutils patch sed grep
+        gawk gnu-gettext hello guile-2.0 guile-2.2 zlib gzip xz
+        %bootstrap-binaries-tarball
+        %binutils-bootstrap-tarball
+        (%glibc-bootstrap-tarball)
+        %gcc-bootstrap-tarball
+        %guile-bootstrap-tarball
+        %bootstrap-tarballs))
+
+(define %packages-to-cross-build
+  %core-packages)
+
+(define %cross-targets
+  '("mips64el-linux-gnu"
+    "mips64el-linux-gnuabi64"
+    "arm-linux-gnueabihf"
+    "aarch64-linux-gnu"
+    "powerpc-linux-gnu"
+    "i586-pc-gnu"                                 ;aka. GNU/Hurd
+    "i686-w64-mingw32"))
+
+(define %guixsd-supported-systems
+  '("x86_64-linux" "i686-linux" "armhf-linux"))
+
+(define %u-boot-systems
+  '("armhf-linux"))
+
+(define (qemu-jobs store system)
+  "Return a list of jobs that build QEMU images for SYSTEM."
+  (define (->alist drv)
+    `((derivation . ,(derivation-file-name drv))
+      (description . "Stand-alone QEMU image of the GNU system")
+      (long-description . "This is a demo stand-alone QEMU image of the GNU
+system.")
+      (license . ,gpl3+)
+      (home-page . ,%guix-home-page-url)
+      (maintainers . ("bug-guix@gnu.org"))))
+
+  (define (->job name drv)
+    (let ((name (symbol-append name (string->symbol ".")
+                               (string->symbol system))))
+      `(,name . ,(lambda ()
+                   (parameterize ((%graft? #f))
+                     (->alist drv))))))
+
+  (define MiB
+    (expt 2 20))
+
+  (if (member system %guixsd-supported-systems)
+      (if (member system %u-boot-systems)
+          (list (->job 'flash-image
+                       (run-with-store store
+                         (mbegin %store-monad
+                           (set-guile-for-build (default-guile))
+                           (system-disk-image
+                            (operating-system (inherit installation-os)
+                             (bootloader (bootloader-configuration
+                                          (bootloader u-boot-bootloader)
+                                          (target #f))))
+                            #:disk-image-size
+                            (* 1024 MiB))))))
+          (list (->job 'usb-image
+                       (run-with-store store
+                         (mbegin %store-monad
+                           (set-guile-for-build (default-guile))
+                           (system-disk-image installation-os
+                                              #:disk-image-size
+                                              (* 1024 MiB)))))
+                (->job 'iso9660-image
+                       (run-with-store store
+                         (mbegin %store-monad
+                           (set-guile-for-build (default-guile))
+                           (system-disk-image installation-os
+                                              #:file-system-type
+                                              "iso9660"))))))
+      '()))
+
+(define (system-test-jobs store system)
+  "Return a list of jobs for the system tests."
+  (define (test->thunk test)
+    (lambda ()
+      (define drv
+        (run-with-store store
+          (mbegin %store-monad
+            (set-current-system system)
+            (set-grafting #f)
+            (set-guile-for-build (default-guile))
+            (system-test-value test))))
+
+      `((derivation . ,(derivation-file-name drv))
+        (description . ,(format #f "GuixSD '~a' system test"
+                                (system-test-name test)))
+        (long-description . ,(system-test-description test))
+        (license . ,gpl3+)
+        (home-page . ,%guix-home-page-url)
+        (maintainers . ("bug-guix@gnu.org")))))
+
+  (define (->job test)
+    (let ((name (string->symbol
+                 (string-append "test." (system-test-name test)
+                                "." system))))
+      (cons name (test->thunk test))))
+
+  (if (member system %guixsd-supported-systems)
+      (map ->job (all-system-tests))
+      '()))
+
+(define (tarball-jobs store system)
+  "Return Hydra jobs to build the self-contained Guix binary tarball."
+  (define (->alist drv)
+    `((derivation . ,(derivation-file-name drv))
+      (description . "Stand-alone binary Guix tarball")
+      (long-description . "This is a tarball containing binaries of Guix and
+all its dependencies, and ready to be installed on non-GuixSD distributions.")
+      (license . ,gpl3+)
+      (home-page . ,%guix-home-page-url)
+      (maintainers . ("bug-guix@gnu.org"))))
+
+  (define (->job name drv)
+    (let ((name (symbol-append name (string->symbol ".")
+                               (string->symbol system))))
+      `(,name . ,(lambda ()
+                   (parameterize ((%graft? #f))
+                     (->alist drv))))))
+
+  ;; XXX: Add a job for the stable Guix?
+  (list (->job 'binary-tarball
+               (run-with-store store
+                 (mbegin %store-monad
+                   (set-guile-for-build (default-guile))
+                   (>>= (profile-derivation (packages->manifest (list guix)))
+                        (lambda (profile)
+                          (self-contained-tarball "guix-binary" profile
+                                                  #:localstatedir? #t
+                                                  #:compressor
+                                                  (lookup-compressor "xz")))))
+                 #:system system))))
+
+(define job-name
+  ;; Return the name of a package's job.
+  (compose string->symbol
+           (cut package-full-name <> "-")))
+
+(define package->job
+  (let ((base-packages
+         (delete-duplicates
+          (append-map (match-lambda
+                       ((_ package _ ...)
+                        (match (package-transitive-inputs package)
+                          (((_ inputs _ ...) ...)
+                           inputs))))
+                      (%final-inputs)))))
+    (lambda (store package system)
+      "Return a job for PACKAGE on SYSTEM, or #f if this combination is not
+valid."
+      (cond ((member package base-packages)
+             (package-job store (symbol-append 'base. (job-name package))
+                          package system))
+            ((supported-package? package system)
+             (let ((drv (package-derivation store package system
+                                            #:graft? #f)))
+               (and (substitutable-derivation? drv)
+                    (package-job store (job-name package)
+                                 package system))))
+            (else
+             #f)))))
+
+(define (all-packages)
+  "Return the list of packages to build."
+  (define (adjust package result)
+    (cond ((package-replacement package)
+           (cons* package                         ;build both
+                  (package-replacement package)
+                  result))
+          ((package-superseded package)
+           result)                                ;don't build it
+          (else
+           (cons package result))))
+
+  (fold-packages adjust
+                 (fold adjust '()                 ;include base packages
+                       (match (%final-inputs)
+                         (((labels packages _ ...) ...)
+                          packages)))
+                 #:select? (const #t)))           ;include hidden packages
+
+(define (arguments->manifests arguments)
+  "Return the list of manifests extracted from ARGUMENTS."
+  (map (match-lambda
+         ((input-name . relative-path)
+          (let* ((checkout (assq-ref arguments (string->symbol input-name)))
+                 (base (assq-ref checkout 'file-name)))
+            (in-vicinity base relative-path))))
+       (assq-ref arguments 'manifests)))
+
+(define (manifests->packages store manifests)
+  "Return the list of packages found in MANIFESTS."
+  (define (load-manifest manifest)
+    (save-module-excursion
+     (lambda ()
+       (set-current-module (make-user-module '((guix profiles) (gnu))))
+       (primitive-load manifest))))
+
+  (delete-duplicates!
+   (map manifest-entry-item
+        (append-map (compose manifest-entries
+                             load-manifest)
+                    manifests))))
+
+
+;;;
+;;; Hydra entry point.
+;;;
+
+(define (hydra-jobs store arguments)
+  "Return Hydra jobs."
+  (define subset
+    (match (assoc-ref arguments 'subset)
+      ("core" 'core)                              ; only build core packages
+      ("hello" 'hello)                            ; only build hello
+      (((? string?) (? string?) ...) 'list)       ; only build selected list of packages
+      ("manifests" 'manifests)                    ; only build packages in the list of manifests
+      (_ 'all)))                                  ; build everything
+
+  (define systems
+    (match (assoc-ref arguments 'systems)
+      (#f              %hydra-supported-systems)
+      ((lst ...)       lst)
+      ((? string? str) (call-with-input-string str read))))
+
+  (define (cross-jobs system)
+    (define (from-32-to-64? target)
+      ;; Return true if SYSTEM is 32-bit and TARGET is 64-bit.  This hack
+      ;; prevents known-to-fail cross-builds from i686-linux or armhf-linux to
+      ;; mips64el-linux-gnuabi64.
+      (and (or (string-prefix? "i686-" system)
+               (string-prefix? "i586-" system)
+               (string-prefix? "armhf-" system))
+           (string-contains target "64")))    ;x86_64, mips64el, aarch64, etc.
+
+    (define (same? target)
+      ;; Return true if SYSTEM and TARGET are the same thing.  This is so we
+      ;; don't try to cross-compile to 'mips64el-linux-gnu' from
+      ;; 'mips64el-linux'.
+      (or (string-contains target system)
+          (and (string-prefix? "armhf" system)    ;armhf-linux
+               (string-prefix? "arm" target))))   ;arm-linux-gnueabihf
+
+    (define (pointless? target)
+      ;; Return #t if it makes no sense to cross-build to TARGET from SYSTEM.
+      (match system
+        ((or "x86_64-linux" "i686-linux")
+         (if (string-contains target "mingw")
+             (not (string=? "x86_64-linux" system))
+             #f))
+        (_
+         ;; Don't try to cross-compile from non-Intel platforms: this isn't
+         ;; very useful and these are often brittle configurations.
+         #t)))
+
+    (define (either proc1 proc2 proc3)
+      (lambda (x)
+        (or (proc1 x) (proc2 x) (proc3 x))))
+
+    (append-map (lambda (target)
+                  (map (lambda (package)
+                         (package-cross-job store (job-name package)
+                                            package target system))
+                       %packages-to-cross-build))
+                (remove (either from-32-to-64? same? pointless?)
+                        %cross-targets)))
+
+  ;; Turn off grafts.  Grafting is meant to happen on the user's machines.
+  (parameterize ((%graft? #f))
+    ;; Return one job for each package, except bootstrap packages.
+    (append-map (lambda (system)
+                  (format (current-error-port)
+                          "evaluating for '~a' (heap size: ~a MiB)...~%"
+                          system
+                          (round
+                           (/ (assoc-ref (gc-stats) 'heap-size)
+                              (expt 2. 20))))
+                  (invalidate-derivation-caches!)
+                  (case subset
+                    ((all)
+                     ;; Build everything, including replacements.
+                     (let ((all (all-packages))
+                           (job (lambda (package)
+                                  (package->job store package
+                                                system))))
+                       (append (filter-map job all)
+                               (qemu-jobs store system)
+                               (system-test-jobs store system)
+                               (tarball-jobs store system)
+                               (cross-jobs system))))
+                    ((core)
+                     ;; Build core packages only.
+                     (append (map (lambda (package)
+                                    (package-job store (job-name package)
+                                                 package system))
+                                  %core-packages)
+                             (cross-jobs system)))
+                    ((hello)
+                     ;; Build hello package only.
+                     (if (string=? system (%current-system))
+                         (let ((hello (specification->package "hello")))
+                           (list (package-job store (job-name hello) hello system)))
+                         '()))
+                    ((list)
+                     ;; Build selected list of packages only.
+                     (if (string=? system (%current-system))
+                         (let* ((names (assoc-ref arguments 'subset))
+                                (packages (map specification->package names)))
+                           (map (lambda (package)
+                                    (package-job store (job-name package)
+                                                 package system))
+                                  packages))
+                         '()))
+                    ((manifests)
+                     ;; Build packages in the list of manifests.
+                     (let* ((manifests (arguments->manifests arguments))
+                            (packages (manifests->packages store manifests)))
+                       (map (lambda (package)
+                              (package-job store (job-name package)
+                                           package system))
+                            packages)))
+                    (else
+                     (error "unknown subset" subset))))
+                systems)))
diff --git a/gnu/local.mk b/gnu/local.mk
index 3350e5abac..1d43250557 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -550,7 +550,9 @@ GNU_SYSTEM_MODULES =				\
   %D%/tests/ssh.scm				\
   %D%/tests/version-control.scm			\
   %D%/tests/virtualization.scm			\
-  %D%/tests/web.scm
+  %D%/tests/web.scm				\
+						\
+  %D%/ci.scm
 
 # Modules that do not need to be compiled.
 MODULES_NOT_COMPILED +=				\
