diff --git a/rust/radix204/Cargo.toml b/rust/radix204/Cargo.toml
new file mode 100644
--- /dev/null
+++ b/rust/radix204/Cargo.toml
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+[package]
+name = "radix204"
+version = "0.1.0"
+
+[dependencies]
+error-chain = "0.11"
+
+[dev-dependencies]
+quickcheck = "0.4"
+rand = "0.3"
+rustc-test = "0.2"
diff --git a/rust/radix204/README.md b/rust/radix204/README.md
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--- /dev/null
+++ b/rust/radix204/README.md
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+# radix204
+
+20-byte to 4-byte mapping using a radix tree stored on plain buffers.
+
+There are 2 plain buffers:
+
+  - KeyBuffer: store 20-bytes keys and look them up using their offsets, read-only to the library.
+  - RadixBuffer: store radix tree nodes and key offsets, managed, read-write by the library.
+
+`radix204` was designed for some specific use-cases efficiently. So it does not have some generic interface, like:
+
+  - Storing extra values
+  - Deletion
+  - Variant-length keys
+  - Long offset (64-bit integer) support
+
+Applications may want to change KeyBuffer format so a `Key` is followed by a `Value` that the application cares about. The `Value` could be a complex structure that includes a deletion flag or a link to another `Value` (linked list).
+
+Variant-length keys and long offsets could in theory be added at the cost of introducing many type parameters (especially around the iterator interface), and double the storage size.
diff --git a/rust/radix204/src/constants.rs b/rust/radix204/src/constants.rs
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--- /dev/null
+++ b/rust/radix204/src/constants.rs
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+// Copyright 2017 Facebook, Inc.
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+use types::KeyId;
+
+pub const KEY_ID_MAX: KeyId = (1 << 31) - 1;
+pub const KEY_LEN: usize = 20;
diff --git a/rust/radix204/src/errors.rs b/rust/radix204/src/errors.rs
new file mode 100644
--- /dev/null
+++ b/rust/radix204/src/errors.rs
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+// Copyright 2017 Facebook, Inc.
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+use types::KeyId;
+
+error_chain! {
+}
diff --git a/rust/radix204/src/lib.rs b/rust/radix204/src/lib.rs
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--- /dev/null
+++ b/rust/radix204/src/lib.rs
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+// Copyright 2017 Facebook, Inc.
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+#[cfg(test)]
+extern crate test;
+
+#[macro_use]
+extern crate error_chain;
+
+#[cfg(test)]
+#[macro_use]
+extern crate quickcheck;
+
+#[cfg(test)]
+extern crate rand;
+
+pub mod types;
+mod constants;
+pub mod errors;
diff --git a/rust/radix204/src/types.rs b/rust/radix204/src/types.rs
new file mode 100644
--- /dev/null
+++ b/rust/radix204/src/types.rs
@@ -0,0 +1,13 @@
+// Copyright 2017 Facebook, Inc.
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+use std::cell::RefCell;
+use std::rc::Rc;
+
+pub type Shared<B> = Rc<RefCell<B>>;
+
+pub type Key = [u8; 20];
+pub type KeyId = u32;
+pub type Offset = KeyId;