diff --git a/alibuild_helpers/build.py b/alibuild_helpers/build.py
index 1a6a9b0c..d5a4bd9d 100644
--- a/alibuild_helpers/build.py
+++ b/alibuild_helpers/build.py
@@ -463,6 +463,13 @@ def doBuild(args, parser):
             ", ".join({x.strip() for x, _ in develPkgsUpper} - set(develPkgs)))
       return 1
 
+  # We must not apply variants to non-development packages (so that the full
+  # package can be downloaded from the remote, for example). Delete the
+  # relevant packages' variants, now that we know the dev packages.
+  for spec in specs.values():
+    if spec["package"] not in develPkgs:
+      spec.pop("variants", None)
+
   if buildOrder:
     banner("Packages will be built in the following order:\n - %s",
            "\n - ".join(x+" (development package)" if x in develPkgs else "%s@%s" % (x, specs[x]["tag"])
@@ -522,6 +529,9 @@ def doBuild(args, parser):
         local_hash, untracked = hash_local_changes(spec)
         untrackedFilesDirectories.extend(untracked)
         spec["devel_hash"] = spec["commit_hash"] + local_hash
+        if spec.get("variants", ()):
+          # spec["variants"] is a set, so its order is undefined. Sort it.
+          spec["devel_hash"] += "/" + ",".join(sorted(spec["variants"]))
         out = spec["scm"].branchOrRef(directory=spec["source"])
         develPackageBranch = out.replace("/", "-")
         spec["tag"] = args.develPrefix if "develPrefix" in args else develPackageBranch
@@ -1068,6 +1078,8 @@ def doBuild(args, parser):
       ("FULL_BUILD_REQUIRES", " ".join(spec["full_build_requires"])),
       ("FULL_REQUIRES", " ".join(spec["full_requires"])),
       ("WRITE_REPO", spec.get("write_repo", source)),
+      # spec["variants"] is a set, so its order is undefined. Sort it.
+      ("ALIBUILD_BUILD_VARIANT", ",".join(sorted(spec.get("variants", ())))),
     ]
     # Add the extra environment as passed from the command line.
     buildEnvironment += [e.partition('=')[::2] for e in args.environment]
diff --git a/alibuild_helpers/utilities.py b/alibuild_helpers/utilities.py
index cd694dfa..b1982139 100644
--- a/alibuild_helpers/utilities.py
+++ b/alibuild_helpers/utilities.py
@@ -365,12 +365,30 @@ def getPackageList(packages, specs, configDir, preferSystem, noSystem,
   packages = packages[:]
   validDefaults = []  # empty list: all OK; None: no valid default; non-empty list: list of valid ones
   while packages:
-    p = packages.pop(0)
+    # Find requested variants of packages.
+    # We only apply variants to development packages (we always store
+    # requested variants here, but delete them from non-dev packages later).
+    # Variants allow building only a subset of a package (e.g. a specific
+    # CMake target), saving build time.
+    p, has_variants, variants = packages.pop(0).partition("#")
+    variants = {var.strip() for var in variants.split(",") if var}
+
     if p in specs:
+      if not has_variants:
+        # If we now want to build without variants (i.e. the whole package),
+        # wipe out any previously-configured variants for this package.
+        specs[p].pop("variants", None)
+      elif specs[p].get("variants"):
+        # The existing package has variants, and this repetition of it does
+        # too. Merge the variants lists.
+        specs[p]["variants"] |= variants
       continue
+
     lowerPkg = p.lower()
     filename = taps.get(lowerPkg, "%s/%s.sh" % (configDir, lowerPkg))
     err, spec, recipe = parseRecipe(getRecipeReader(filename, configDir))
+    if has_variants and variants:
+      spec["variants"] = variants
     dieOnError(err, err)
     dieOnError(spec["package"].lower() != lowerPkg,
                "%s.sh has different package field: %s" % (p, spec["package"]))