diff --git a/src/board/castle_rights.rs b/src/board/castle_rights.rs
new file mode 100644
index 0000000..9ea7ad6
--- /dev/null
+++ b/src/board/castle_rights.rs
@@ -0,0 +1,55 @@
+/// Current castle rights for a player.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum CastleRights {
+    /// No castling allowed.
+    NoSide,
+    /// King-side castling only.
+    KingSide,
+    /// Queen-side castling only.
+    QueenSide,
+    /// Either side allowed.
+    BothSides,
+}
+
+impl CastleRights {
+    /// Convert from a castle rights index into a [CastleRights] type.
+    #[inline(always)]
+    pub fn from_index(index: usize) -> Self {
+        assert!(index < 4);
+        // SAFETY: we know the value is in-bounds
+        unsafe { Self::from_index_unchecked(index) }
+    }
+
+    /// Convert from a castle rights index into a [CastleRights] type, no bounds checking.
+    #[inline(always)]
+    pub unsafe fn from_index_unchecked(index: usize) -> Self {
+        std::mem::transmute(index as u8)
+    }
+
+    /// Return the index of a given [CastleRights].
+    #[inline(always)]
+    pub fn index(self) -> usize {
+        self as usize
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn from_index() {
+        assert_eq!(CastleRights::from_index(0), CastleRights::NoSide);
+        assert_eq!(CastleRights::from_index(1), CastleRights::KingSide);
+        assert_eq!(CastleRights::from_index(2), CastleRights::QueenSide);
+        assert_eq!(CastleRights::from_index(3), CastleRights::BothSides);
+    }
+
+    #[test]
+    fn index() {
+        assert_eq!(CastleRights::NoSide.index(), 0);
+        assert_eq!(CastleRights::KingSide.index(), 1);
+        assert_eq!(CastleRights::QueenSide.index(), 2);
+        assert_eq!(CastleRights::BothSides.index(), 3);
+    }
+}
diff --git a/src/board/mod.rs b/src/board/mod.rs
index 6a29cbe..ad91192 100644
--- a/src/board/mod.rs
+++ b/src/board/mod.rs
@@ -1,6 +1,9 @@
 pub mod bitboard;
 pub use bitboard::*;
 
+pub mod castle_rights;
+pub use castle_rights::*;
+
 pub mod color;
 pub use color::*;