diff --git a/src/board/castle_rights.rs b/src/board/castle_rights.rs
new file mode 100644
index 0000000..0e44e03
--- /dev/null
+++ b/src/board/castle_rights.rs
@@ -0,0 +1,196 @@
+use super::{Bitboard, Color, File, Square};
+
+/// 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
+    }
+
+    /// Can the player castle king-side.
+    #[inline(always)]
+    pub fn has_king_side(self) -> bool {
+        (self.index() & 1) != 0
+    }
+
+    /// Can the player castle king-side.
+    #[inline(always)]
+    pub fn has_queen_side(self) -> bool {
+        (self.index() & 2) != 0
+    }
+
+    /// Remove king-side castling rights.
+    #[inline(always)]
+    pub fn without_king_side(self) -> Self {
+        self.remove(Self::KingSide)
+    }
+
+    /// Remove queen-side castling rights.
+    #[inline(always)]
+    pub fn without_queen_side(self) -> Self {
+        self.remove(Self::QueenSide)
+    }
+
+    /// Remove some [CastleRights], and return the resulting [CastleRights].
+    #[inline(always)]
+    pub fn remove(self, to_remove: CastleRights) -> Self {
+        // SAFETY: we know the value is in-bounds
+        unsafe { Self::from_index_unchecked(self.index() & !to_remove.index()) }
+    }
+
+    /// Which rooks have not been moved for a given [CastleRights] and [Color].
+    #[inline(always)]
+    pub fn unmoved_rooks(self, color: Color) -> Bitboard {
+        let rank = color.first_rank();
+
+        let king_side_square = Square::new(File::H, rank);
+        let queen_side_square = Square::new(File::A, rank);
+
+        match self {
+            Self::NoSide => Bitboard::EMPTY,
+            Self::KingSide => king_side_square.into_bitboard(),
+            Self::QueenSide => queen_side_square.into_bitboard(),
+            Self::BothSides => king_side_square | queen_side_square,
+        }
+    }
+}
+
+#[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);
+    }
+
+    #[test]
+    fn has_kingside() {
+        assert!(!CastleRights::NoSide.has_king_side());
+        assert!(!CastleRights::QueenSide.has_king_side());
+        assert!(CastleRights::KingSide.has_king_side());
+        assert!(CastleRights::BothSides.has_king_side());
+    }
+
+    #[test]
+    fn has_queenside() {
+        assert!(!CastleRights::NoSide.has_queen_side());
+        assert!(!CastleRights::KingSide.has_queen_side());
+        assert!(CastleRights::QueenSide.has_queen_side());
+        assert!(CastleRights::BothSides.has_queen_side());
+    }
+
+    #[test]
+    fn without_king_side() {
+        assert_eq!(
+            CastleRights::NoSide.without_king_side(),
+            CastleRights::NoSide
+        );
+        assert_eq!(
+            CastleRights::KingSide.without_king_side(),
+            CastleRights::NoSide
+        );
+        assert_eq!(
+            CastleRights::QueenSide.without_king_side(),
+            CastleRights::QueenSide
+        );
+        assert_eq!(
+            CastleRights::BothSides.without_king_side(),
+            CastleRights::QueenSide
+        );
+    }
+
+    #[test]
+    fn without_queen_side() {
+        assert_eq!(
+            CastleRights::NoSide.without_queen_side(),
+            CastleRights::NoSide
+        );
+        assert_eq!(
+            CastleRights::QueenSide.without_queen_side(),
+            CastleRights::NoSide
+        );
+        assert_eq!(
+            CastleRights::KingSide.without_queen_side(),
+            CastleRights::KingSide
+        );
+        assert_eq!(
+            CastleRights::BothSides.without_queen_side(),
+            CastleRights::KingSide
+        );
+    }
+
+    #[test]
+    fn unmoved_rooks() {
+        assert_eq!(
+            CastleRights::NoSide.unmoved_rooks(Color::White),
+            Bitboard::EMPTY
+        );
+        assert_eq!(
+            CastleRights::NoSide.unmoved_rooks(Color::Black),
+            Bitboard::EMPTY
+        );
+        assert_eq!(
+            CastleRights::KingSide.unmoved_rooks(Color::White),
+            Square::H1.into_bitboard()
+        );
+        assert_eq!(
+            CastleRights::KingSide.unmoved_rooks(Color::Black),
+            Square::H8.into_bitboard()
+        );
+        assert_eq!(
+            CastleRights::QueenSide.unmoved_rooks(Color::White),
+            Square::A1.into_bitboard()
+        );
+        assert_eq!(
+            CastleRights::QueenSide.unmoved_rooks(Color::Black),
+            Square::A8.into_bitboard()
+        );
+        assert_eq!(
+            CastleRights::BothSides.unmoved_rooks(Color::White),
+            Square::A1 | Square::H1
+        );
+        assert_eq!(
+            CastleRights::BothSides.unmoved_rooks(Color::Black),
+            Square::A8 | Square::H8
+        );
+    }
+}
diff --git a/src/board/color.rs b/src/board/color.rs
new file mode 100644
index 0000000..a7af8b6
--- /dev/null
+++ b/src/board/color.rs
@@ -0,0 +1,102 @@
+use super::Rank;
+
+/// An enum representing the color of a player.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum Color {
+    White,
+    Black,
+}
+
+impl Color {
+    /// Convert from a file index into a [Color] type.
+    #[inline(always)]
+    pub fn from_index(index: usize) -> Self {
+        assert!(index < 2);
+        // SAFETY: we know the value is in-bounds
+        unsafe { Self::from_index_unchecked(index) }
+    }
+
+    /// Convert from a file index into a [Color] 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 [Color].
+    #[inline(always)]
+    pub fn index(self) -> usize {
+        self as usize
+    }
+
+    /// Return the first [Rank] for pieces of the given [Color], where its pieces start.
+    #[inline(always)]
+    pub fn first_rank(self) -> Rank {
+        match self {
+            Self::White => Rank::First,
+            Self::Black => Rank::Eighth,
+        }
+    }
+
+    /// Return the second [Rank] for pieces of the given [Color], where its pawns start.
+    #[inline(always)]
+    pub fn second_rank(self) -> Rank {
+        match self {
+            Self::White => Rank::Second,
+            Self::Black => Rank::Seventh,
+        }
+    }
+
+    /// Return the fourth [Rank] for pieces of the given [Color], where its pawns move to after a
+    /// two-square move.
+    #[inline(always)]
+    pub fn fourth_rank(self) -> Rank {
+        match self {
+            Self::White => Rank::Fourth,
+            Self::Black => Rank::Fifth,
+        }
+    }
+
+    /// Return the seventh [Rank] for pieces of the given [Color], which is the rank before a pawn
+    /// gets promoted.
+    #[inline(always)]
+    pub fn seventh_rank(self) -> Rank {
+        match self {
+            Self::White => Rank::Seventh,
+            Self::Black => Rank::Second,
+        }
+    }
+}
+
+impl std::ops::Not for Color {
+    type Output = Color;
+
+    fn not(self) -> Self::Output {
+        match self {
+            Self::White => Self::Black,
+            Self::Black => Self::White,
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn from_index() {
+        assert_eq!(Color::from_index(0), Color::White);
+        assert_eq!(Color::from_index(1), Color::Black);
+    }
+
+    #[test]
+    fn index() {
+        assert_eq!(Color::White.index(), 0);
+        assert_eq!(Color::Black.index(), 1);
+    }
+
+    #[test]
+    fn not() {
+        assert_eq!(!Color::White, Color::Black);
+        assert_eq!(!Color::Black, Color::White);
+    }
+}
diff --git a/src/board/directions.rs b/src/board/direction.rs
similarity index 100%
rename from src/board/directions.rs
rename to src/board/direction.rs
diff --git a/src/board/mod.rs b/src/board/mod.rs
index bc9d1d9..ad91192 100644
--- a/src/board/mod.rs
+++ b/src/board/mod.rs
@@ -1,8 +1,14 @@
 pub mod bitboard;
 pub use bitboard::*;
 
-pub mod directions;
-pub use directions::*;
+pub mod castle_rights;
+pub use castle_rights::*;
+
+pub mod color;
+pub use color::*;
+
+pub mod direction;
+pub use direction::*;
 
 pub mod file;
 pub use file::*;