diff --git a/.gitignore b/.gitignore
index b8bff339e..83622b14a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,3 +19,4 @@ a.out
 
 # direnv Nix stuff
 .direnv/
+reference-code/
diff --git a/README.md b/README.md
index f123c27a6..b4fcdabd8 100644
--- a/README.md
+++ b/README.md
@@ -81,6 +81,7 @@ CGO_ENABLED=0 go build ./types
 This package contains the code binding the libwasmvm build to the Go code. All
 low level FFI handling code belongs there. This package can only be built using
 cgo. Using the `internal/` convention makes this package fully private.
+For an overview of the exported C functions and their Go wrappers see [docs/CGO_INTERFACE.md](docs/CGO_INTERFACE.md).
 
 #### Package github.com/CosmWasm/wasmvm
 
diff --git a/docs/CGO_INTERFACE.md b/docs/CGO_INTERFACE.md
new file mode 100644
index 000000000..eea2170db
--- /dev/null
+++ b/docs/CGO_INTERFACE.md
@@ -0,0 +1,61 @@
+# CGO interface
+
+This document summarises the functions exported by the `libwasmvm` C library and their
+wrappers implemented in the Go package `internal/api`. It also lists the Go data
+structures from `types/` that cross the cgo boundary.
+
+## Exported functions and Go wrappers
+
+| C function (bindings.h) | Go wrapper |
+| --- | --- |
+| `init_cache` | `api.InitCache` |
+| `store_code` | `api.StoreCode`/`api.StoreCodeUnchecked` |
+| `remove_wasm` | `api.RemoveCode` |
+| `load_wasm` | `api.GetCode` |
+| `pin` | `api.Pin` |
+| `unpin` | `api.Unpin` |
+| `analyze_code` | `api.AnalyzeCode` |
+| `get_metrics` | `api.GetMetrics` |
+| `get_pinned_metrics` | `api.GetPinnedMetrics` |
+| `release_cache` | `api.ReleaseCache` |
+| `instantiate` | `api.Instantiate` |
+| `execute` | `api.Execute` |
+| `migrate` | `api.Migrate` |
+| `migrate_with_info` | `api.MigrateWithInfo` |
+| `sudo` | `api.Sudo` |
+| `reply` | `api.Reply` |
+| `query` | `api.Query` |
+| `ibc_channel_open` | `api.IBCChannelOpen` |
+| `ibc_channel_connect` | `api.IBCChannelConnect` |
+| `ibc_channel_close` | `api.IBCChannelClose` |
+| `ibc_packet_receive` | `api.IBCPacketReceive` |
+| `ibc_packet_ack` | `api.IBCPacketAck` |
+| `ibc_packet_timeout` | `api.IBCPacketTimeout` |
+| `ibc_source_callback` | `api.IBCSourceCallback` |
+| `ibc_destination_callback` | `api.IBCDestinationCallback` |
+| `ibc2_packet_receive` | `api.IBC2PacketReceive` |
+| `ibc2_packet_ack` | `api.IBC2PacketAck` |
+| `ibc2_packet_timeout` | `api.IBC2PacketTimeout` |
+| `ibc2_packet_send` | `api.IBC2PacketSend` |
+| `new_unmanaged_vector` | internal helpers in `memory.go` |
+| `destroy_unmanaged_vector` | internal helpers in `memory.go` |
+| `version_str` | `api.LibwasmvmVersion` |
+
+## Data structures crossing the boundary
+
+Several types defined in the `types` package are used when calling into
+`libwasmvm` or when reading its results:
+
+- `VMConfig` – configuration passed to `InitCache`.
+- `GasMeter` – interface supplying gas information for execution.
+- `KVStore` and `Iterator` – database interface used by the VM.
+- `GoAPI` – set of callbacks for address handling.
+- `Querier` – interface for custom queries.
+- `AnalysisReport` – returned from `AnalyzeCode`.
+- `Metrics` and `PinnedMetrics` – returned from metric queries.
+- `GasReport` – returned from execution functions.
+
+All other data (such as contract messages, environment and info values) is
+passed as byte slices and therefore does not rely on additional exported Go
+structures.
+