diff --git a/build/README.md b/build/README.md
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+# `//build`
+
+This directory contains global build and CI infrastructure which are useful across the entire monorepo, such as toolchains, Bazel libraries and CI config.
+
diff --git a/cloud/README.md b/cloud/README.md
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+# `//cloud`
+
+`//cloud` contains tooling and libraries for orchestrating Monogon OS clusters.
diff --git a/go/README.md b/go/README.md
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+# `//go`
+
+Go libraries which are not specific to any component live here. For example, this is a good place to put algorithms or helper libraries.
diff --git a/intellij/README.md b/intellij/README.md
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+++ b/intellij/README.md
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+# `//intellij`
+
+Supporting infrastructure for using the Bazel IntelliJ plugin with our monorepo.
diff --git a/net/README.md b/net/README.md
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+++ b/net/README.md
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+# `//net`
+
+API definitions and tooling for Monogon OS network definitions. It currently happens to live at the top level because it is shared between //cloud and //metropolis, we should find a more sensible place for it.
diff --git a/osbase/README.md b/osbase/README.md
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+++ b/osbase/README.md
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+# `//osbase`
+
+osbase is our SDK for building an operating system. It contains low-level building blocks for making a "mini OS" such as ktest, the cloud agent or Monogon OS itself.
diff --git a/third_party/README.md b/third_party/README.md
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+++ b/third_party/README.md
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+# `//third_party`
+
+Anything related to importing third party code and making it work with our monorepo lives here:
+
+- Vendored code.
+- Bazel rules for third party code.
+- Patches to thid party code.
+- Lock files and similar package manager definitions (whenever possible - things like `go.mod  have to live at the top level, and that's OK too).
+
+First-party code or build rules based *on* a third-party component should not live here.