diff --git a/Cargo.lock b/Cargo.lock
index cbc8dab..847817b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -147,4 +147,9 @@ dependencies = [
  "snafu",
  "usize_conversions",
  "ux",
+ "vesper-user",
 ]
+
+[[package]]
+name = "vesper-user"
+version = "0.0.1"
diff --git a/Cargo.toml b/Cargo.toml
index 064e5e9..ef6702d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,7 @@
 [workspace]
 members = [
     "nucleus",
+    "vesper-user",
     "crates/tock-registers"
 ]
 
diff --git a/nucleus/Cargo.toml b/nucleus/Cargo.toml
index 7af8db0..af7e5da 100644
--- a/nucleus/Cargo.toml
+++ b/nucleus/Cargo.toml
@@ -4,7 +4,7 @@ version = "0.0.1"
 authors = ["Berkus Decker <berkus+vesper@metta.systems>"]
 description = "Vesper exokernel"
 documentation = "https://docs.metta.systems/vesper"
-homepage = "https://github.com/metta-systems/vesper"
+homepage = "https://metta.systems/products/vesper"
 repository = "https://github.com/metta-systems/vesper"
 readme = "README.md"
 license = "BlueOak-1.0.0"
@@ -38,6 +38,7 @@ bitflags = "1.2.1"
 cfg-if = "1.0"
 snafu = { version = "0.6", default-features = false }
 paste = "1.0"
+vesper-user = { path = "../vesper-user" }
 
 #embedded-serial = "0.5.0"
 # jlink_rtt = { version = "0.1.0", optional = true }
diff --git a/nucleus/README.md b/nucleus/README.md
new file mode 100644
index 0000000..c4ae5bc
--- /dev/null
+++ b/nucleus/README.md
@@ -0,0 +1,7 @@
+# Vesper Kernel
+
+This directory contains binary for the vesper kernel.
+
+----
+
+For more information please re-read.
diff --git a/nucleus/src/api.rs b/nucleus/src/api.rs
index ef22fcb..db9efab 100644
--- a/nucleus/src/api.rs
+++ b/nucleus/src/api.rs
@@ -8,6 +8,8 @@
 //! Arch-specific kernel ABI decodes syscall invocations and calls API functions to perform actual
 //! operations.
 
+use vesper_user::SysCall as SysCall;
+
 // Syscalls (kernel API)
 trait API {
     // Three below (send, nb_send, call) are "invocation" syscalls.
@@ -45,18 +47,6 @@ trait API {
     // Plus some debugging calls...
 }
 
-// @todo This is going to be in the interface library.
-enum SysCall {
-    Send,
-    NBSend,
-    Call,
-    Recv,
-    Reply,
-    ReplyRecv,
-    NBRecv,
-    Yield,
-}
-
 fn handle_syscall(syscall: SysCall) -> Result<()> {
     match syscall {
         SysCall::Send => {
diff --git a/vesper-user/Cargo.toml b/vesper-user/Cargo.toml
new file mode 100644
index 0000000..65a543b
--- /dev/null
+++ b/vesper-user/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "vesper-user"
+version = "0.0.1"
+authors = ["Berkus Decker <berkus+vesper@metta.systems>"]
+description = "Vesper user-space interface"
+documentation = "https://docs.metta.systems/vesper-user"
+homepage = "https://metta.systems/products/vesper"
+repository = "https://github.com/metta-systems/vesper"
+readme = "README.md"
+license = "BlueOak-1.0.0"
+categories = ["no-std", "embedded", "os"]
+publish = false
+edition = "2018"
+
+[badges]
+maintenance = { status = "experimental" }
+
+[dependencies]
diff --git a/vesper-user/README.md b/vesper-user/README.md
new file mode 100644
index 0000000..cfcad8d
--- /dev/null
+++ b/vesper-user/README.md
@@ -0,0 +1,8 @@
+# User-space Kernel Interface
+
+This directory contains library for interfacing with the kernel through syscalls.
+This library also defines constants and types shared between kernel- and user-space.
+
+----
+
+For more information please re-read.
diff --git a/vesper-user/src/arch/aarch64/mod.rs b/vesper-user/src/arch/aarch64/mod.rs
new file mode 100644
index 0000000..6285171
--- /dev/null
+++ b/vesper-user/src/arch/aarch64/mod.rs
@@ -0,0 +1 @@
+pub mod syscall;
diff --git a/vesper-user/src/arch/aarch64/syscall.rs b/vesper-user/src/arch/aarch64/syscall.rs
new file mode 100644
index 0000000..5e4aace
--- /dev/null
+++ b/vesper-user/src/arch/aarch64/syscall.rs
@@ -0,0 +1,3 @@
+pub fn syscall(number: u64) {
+    asm!("svc #1234")
+}
diff --git a/vesper-user/src/arch/mod.rs b/vesper-user/src/arch/mod.rs
new file mode 100644
index 0000000..aeec869
--- /dev/null
+++ b/vesper-user/src/arch/mod.rs
@@ -0,0 +1,10 @@
+/*
+ * SPDX-License-Identifier: BlueOak-1.0.0
+ * Copyright (c) Berkus Decker <berkus+vesper@metta.systems>
+ */
+
+#[cfg(target_arch = "aarch64")]
+#[macro_use]
+pub mod aarch64;
+#[cfg(target_arch = "aarch64")]
+pub use self::aarch64::*;
diff --git a/vesper-user/src/lib.rs b/vesper-user/src/lib.rs
new file mode 100644
index 0000000..a1e29d7
--- /dev/null
+++ b/vesper-user/src/lib.rs
@@ -0,0 +1,20 @@
+pub mod arch;
+
+pub use arch::syscall;
+
+pub enum SysCall {
+    Send,
+    NBSend,
+    Call,
+    Recv,
+    Reply,
+    ReplyRecv,
+    NBRecv,
+    Yield,
+}
+
+#[cfg(test)]
+mod tests {
+    #[test_case]
+    fn test_debug_output_syscall() {}
+}