diff --git a/src/board/chess_board/error.rs b/src/board/chess_board/error.rs
new file mode 100644
index 0000000..e531f54
--- /dev/null
+++ b/src/board/chess_board/error.rs
@@ -0,0 +1,50 @@
+/// A singular type for all errors that could happen during [ChessBoard::is_valid].
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum InvalidError {
+    /// Too many pieces.
+    TooManyPieces,
+    /// Missing king.
+    MissingKing,
+    /// Pawns on the first/last rank.
+    InvalidPawnPosition,
+    /// Castling rights do not match up with the state of the board.
+    InvalidCastlingRights,
+    /// En-passant target square is not empty and behind an opponent's pawn.
+    InvalidEnPassant,
+    /// The two kings are next to each other.
+    NeighbouringKings,
+    /// The opponent is currently in check.
+    OpponentInCheck,
+    /// The piece-specific boards are overlapping.
+    OverlappingPieces,
+    /// The color-specific boards are overlapping.
+    OverlappingColors,
+    /// The pre-computed combined occupancy boards does not match the other boards.
+    ErroneousCombinedOccupancy,
+}
+
+impl std::fmt::Display for InvalidError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let error_msg = match self {
+            Self::TooManyPieces => "Too many pieces.",
+            Self::MissingKing => "Missing king.",
+            Self::InvalidPawnPosition => "Pawns on the first/last rank.",
+            Self::InvalidCastlingRights => {
+                "Castling rights do not match up with the state of the board."
+            }
+            Self::InvalidEnPassant => {
+                "En-passant target square is not empty and behind an opponent's pawn."
+            }
+            Self::NeighbouringKings => "The two kings are next to each other.",
+            Self::OpponentInCheck => "The opponent is currently in check.",
+            Self::OverlappingPieces => "The piece-specific boards are overlapping.",
+            Self::OverlappingColors => "The color-specific boards are overlapping.",
+            Self::ErroneousCombinedOccupancy => {
+                "The pre-computed combined occupancy boards does not match the other boards."
+            }
+        };
+        write!(f, "{}", error_msg)
+    }
+}
+
+impl std::error::Error for InvalidError {}
diff --git a/src/board/chess_board/mod.rs b/src/board/chess_board/mod.rs
index 838769a..17d34e8 100644
--- a/src/board/chess_board/mod.rs
+++ b/src/board/chess_board/mod.rs
@@ -5,6 +5,9 @@ use crate::{
 
 use super::{Bitboard, CastleRights, Color, File, Move, Piece, Rank, Square};
 
+mod error;
+pub use error::*;
+
 /// Represent an on-going chess game.
 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub struct ChessBoard {