diff --git a/compiler/rustc_smir/.gitignore b/compiler/rustc_smir/.gitignore
new file mode 100644
index 00000000000..eb5a316cbd1
--- /dev/null
+++ b/compiler/rustc_smir/.gitignore
@@ -0,0 +1 @@
+target
diff --git a/compiler/rustc_smir/Cargo.toml b/compiler/rustc_smir/Cargo.toml
new file mode 100644
index 00000000000..bc0cac5a0bc
--- /dev/null
+++ b/compiler/rustc_smir/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "rustc_smir"
+version = "0.0.0"
+edition = "2021"
+
+[dependencies]
+rustc_middle = { path = "../rustc_middle", optional = true }
+rustc_driver = { path = "../rustc_driver", optional = true }
+rustc_borrowck = { path = "../rustc_borrowck", optional = true }
+rustc_interface = { path = "../rustc_interface", optional = true }
+
+[features]
+default = ["rustc_middle", "rustc_driver", "rustc_borrowck", "rustc_interface"]
diff --git a/compiler/rustc_smir/README.md b/compiler/rustc_smir/README.md
new file mode 100644
index 00000000000..ae49098dd0c
--- /dev/null
+++ b/compiler/rustc_smir/README.md
@@ -0,0 +1,75 @@
+This crate is regularly synced with its mirror in the rustc repo at `compiler/rustc_smir`.
+
+We use `git subtree` for this to preserve commits and allow the rustc repo to
+edit these crates without having to touch this repo. This keeps the crates compiling
+while allowing us to independently work on them here. The effort of keeping them in
+sync is pushed entirely onto us, without affecting rustc workflows negatively.
+This may change in the future, but changes to policy should only be done via a
+compiler team MCP.
+
+## Instructions for working on this crate locally
+
+Since the crate is the same in the rustc repo and here, the dependencies on rustc_* crates
+will only either work here or there, but never in both places at the same time. Thus we use
+optional dependencies on the rustc_* crates, requiring local development to use
+
+```
+cargo build --no-default-features -Zavoid-dev-deps
+```
+
+in order to compile successfully.
+
+## Instructions for syncing
+
+### Updating this repository
+
+In the rustc repo, execute
+
+```
+git subtree push --prefix=compiler/rustc_smir url_to_your_fork_of_project_stable_mir some_feature_branch
+```
+
+and then open a PR of your `some_feature_branch` against https://github.com/rust-lang/project-stable-mir
+
+### Updating the rustc library
+
+First we need to bump our stack limit, as the rustc repo otherwise quickly hits that:
+
+```
+ulimit -s 60000
+```
+
+#### Maximum function recursion depth (1000) reached
+
+Then we need to disable `dash` as the default shell for sh scripts, as otherwise we run into a
+hard limit of a recursion depth of 1000:
+
+```
+sudo dpkg-reconfigure dash
+```
+
+and then select `No` to disable dash.
+
+
+#### Patching your `git worktree`
+
+The regular git worktree does not scale to repos of the size of the rustc repo.
+So download the `git-subtree.sh` from https://github.com/gitgitgadget/git/pull/493/files and run
+
+```
+sudo cp --backup /path/to/patched/git-subtree.sh /usr/lib/git-core/git-subtree
+sudo chmod --reference=/usr/lib/git-core/git-subtree~ /usr/lib/git-core/git-subtree
+sudo chown --reference=/usr/lib/git-core/git-subtree~ /usr/lib/git-core/git-subtree
+```
+
+#### Actually doing a sync
+
+In the rustc repo, execute
+
+```
+git subtree pull --prefix=compiler/rustc_smir https://github.com/rust-lang/project-stable-mir smir
+```
+
+Note: only ever sync to rustc from the project-stable-mir's `smir` branch. Do not sync with your own forks.
+
+Then open a PR against rustc just like a regular PR.
diff --git a/compiler/rustc_smir/rust-toolchain.toml b/compiler/rustc_smir/rust-toolchain.toml
new file mode 100644
index 00000000000..7b696fc1f5c
--- /dev/null
+++ b/compiler/rustc_smir/rust-toolchain.toml
@@ -0,0 +1,3 @@
+[toolchain]
+channel = "nightly-2022-06-01"
+components = [ "rustfmt", "rustc-dev" ]
diff --git a/compiler/rustc_smir/src/lib.rs b/compiler/rustc_smir/src/lib.rs
new file mode 100644
index 00000000000..decdae953d9
--- /dev/null
+++ b/compiler/rustc_smir/src/lib.rs
@@ -0,0 +1,18 @@
+//! The WIP stable interface to rustc internals.
+//!
+//! For more information see https://github.com/rust-lang/project-stable-mir
+//!
+//! # Note
+//!
+//! This API is still completely unstable and subject to change.
+
+#![doc(
+    html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
+    test(attr(allow(unused_variables), deny(warnings)))
+)]
+
+#![cfg_attr(not(feature = "default"), feature(rustc_private))]
+
+pub mod mir;
+
+pub mod very_unstable;
diff --git a/compiler/rustc_smir/src/mir.rs b/compiler/rustc_smir/src/mir.rs
new file mode 100644
index 00000000000..855605b1a4f
--- /dev/null
+++ b/compiler/rustc_smir/src/mir.rs
@@ -0,0 +1,10 @@
+pub use crate::very_unstable::middle::mir::{
+    visit::MutVisitor, AggregateKind, AssertKind, BasicBlock, BasicBlockData, BinOp, BindingForm,
+    BlockTailInfo, Body, BorrowKind, CastKind, ClearCrossCrate, Constant, ConstantKind,
+    CopyNonOverlapping, Coverage, FakeReadCause, Field, GeneratorInfo, ImplicitSelfKind,
+    InlineAsmOperand, Local, LocalDecl, LocalInfo, LocalKind, Location, MirPhase, MirSource,
+    NullOp, Operand, Place, PlaceRef, ProjectionElem, ProjectionKind, Promoted, RetagKind, Rvalue,
+    Safety, SourceInfo, SourceScope, SourceScopeData, SourceScopeLocalData, Statement,
+    StatementKind, UnOp, UserTypeProjection, UserTypeProjections, VarBindingForm, VarDebugInfo,
+    VarDebugInfoContents,
+};
diff --git a/compiler/rustc_smir/src/very_unstable.rs b/compiler/rustc_smir/src/very_unstable.rs
new file mode 100644
index 00000000000..12ba133dbb1
--- /dev/null
+++ b/compiler/rustc_smir/src/very_unstable.rs
@@ -0,0 +1,27 @@
+//! This module reexports various crates and modules from unstable rustc APIs.
+//! Add anything you need here and it will get slowly transferred to a stable API.
+//! Only use rustc_smir in your dependencies and use the reexports here instead of
+//! directly referring to the unstable crates.
+
+macro_rules! crates {
+    ($($rustc_name:ident -> $name:ident,)*) => {
+        $(
+            #[cfg(not(feature = "default"))]
+            pub extern crate $rustc_name as $name;
+            #[cfg(feature = "default")]
+            pub use $rustc_name as $name;
+        )*
+    }
+}
+
+crates! {
+    rustc_borrowck -> borrowck,
+    rustc_driver -> driver,
+    rustc_hir -> hir,
+    rustc_interface -> interface,
+    rustc_middle -> middle,
+    rustc_mir_dataflow -> dataflow,
+    rustc_mir_transform -> transform,
+    rustc_serialize -> serialize,
+    rustc_trait_selection -> trait_selection,
+}