diff --git a/build/toolchain/BUILD b/build/toolchain/BUILD
new file mode 100644
index 0000000..5bf53d2
--- /dev/null
+++ b/build/toolchain/BUILD
@@ -0,0 +1,51 @@
+load(":cc_toolchain_config.bzl", "host_cc_toolchain_config")
+
+# Toolchain definitions.
+#
+# We currently define a single custom toolchain: the host_cc toolchain suite.
+# This is a C++ toolchain that uses GCC from the host at hardcoded paths. We
+# can get away with this, as currently the entire build is performed in a known
+# container (see: //scripts:create_container.sh). We define this toolchain so
+# that we have full control over all configuration of it, which we need as we
+# are building some fairly odd C binaries (notably, a qboot bootloader for
+# testing).
+#
+# The host_cc toolchain suite is enabled for all cc_* targets that aren't
+# building host tools by setting --crosstool_top in .bazelrc. In the future,
+# this should only be triggered by transitions where necessary.
+#
+# In the future, the host_cc toolchains should be replaced by a hermetic
+# toolchain that's built locally, or downloaded from the Internet - as
+# github.com/bazelbuild/bazel-toolchains does it. As that's being built, we
+# should then also have another toolchain definition for C binaries that
+# target Smalltown static binaries, so that mkfs.xfs can be built using native
+# cc_* rules, too.
+#
+# This, and :cc_toolchain_config.bzl is based on the following tutorial:
+# https://docs.bazel.build/versions/master/tutorial/cc-toolchain-config.html
+
+package(default_visibility = ["//visibility:public"])
+
+filegroup(name = "empty")
+
+cc_toolchain_suite(
+    name = "host_cc_suite",
+    toolchains = {
+        "k8": ":host_cc_k8_toolchain",
+    },
+)
+
+cc_toolchain(
+    name = "host_cc_k8_toolchain",
+    toolchain_identifier = "host-k8-toolchain",
+    toolchain_config = ":host_cc_k8_toolchain_config",
+    all_files = ":empty",
+    compiler_files = ":empty",
+    dwp_files = ":empty",
+    linker_files = ":empty",
+    objcopy_files = ":empty",
+    strip_files = ":empty",
+    supports_param_files = 0,
+)
+
+host_cc_toolchain_config(name = "host_cc_k8_toolchain_config")