diff --git a/chess/board.go b/chess/board.go
index 03927e1..78e95e1 100644
--- a/chess/board.go
+++ b/chess/board.go
@@ -269,19 +269,22 @@ func (b *Board) Parse(pgn string) error {
 	return nil
 }
 
-func (b *Board) Move(position string) error {
+func (b *Board) Move(move string) error {
 	var (
-		err error
+		piece          string
+		targetPosition string
 		// the column from which the piece is captured.
 		// for example, this would be 'e' for exd4 and 'e' for Nexd4.
-		captureFrom string
+		captureFrom    string
+		collisionPiece *Piece
+		err            error
 	)
 
-	if strings.Contains(position, "x") {
+	if strings.Contains(move, "x") {
 		// capture move
-		parts := strings.Split(position, "x")
+		parts := strings.Split(move, "x")
 		if len(parts) != 2 {
-			return fmt.Errorf("invalid move: %s", position)
+			return fmt.Errorf("invalid move: %s", move)
 		}
 		if len(parts[0]) == 2 {
 			// example: Nexd4
@@ -295,10 +298,10 @@ func (b *Board) Move(position string) error {
 				captureFrom = ""
 			}
 		} else {
-			return fmt.Errorf("invalid move: %s", position)
+			return fmt.Errorf("invalid move: %s", move)
 		}
 
-		position = strings.Replace(position, captureFrom+"x", "", 1)
+		move = strings.Replace(move, captureFrom+"x", "", 1)
 	}
 
 	// TODO: parse captures e.g. exd5 or Nxd5
@@ -310,25 +313,36 @@ func (b *Board) Move(position string) error {
 	// TODO: make sure king is not in check after move
 	//   ( this avoids moving into check and moving a piece that exposes the king to check e.g. pinned pieces )
 
-	if len(position) == 2 {
-		err = b.movePawn(position, captureFrom)
-	} else if len(position) == 3 {
-		switch strings.ToLower(position[0:1]) {
+	if len(move) == 2 {
+		err = b.movePawn(move, captureFrom)
+	} else if len(move) == 3 {
+
+		piece = move[0:1]
+		targetPosition = move[1:3]
+
+		// collision detection
+		if collisionPiece, err = b.getCollision(targetPosition); err != nil {
+			return fmt.Errorf("invalid move %s: %v", move, err)
+		} else if collisionPiece != nil {
+			return fmt.Errorf("invalid move %s: position %s blocked by %s", move, targetPosition, collisionPiece)
+		}
+
+		switch strings.ToLower(piece) {
 		case "r":
-			err = b.moveRook(position[1:3], false)
+			err = b.moveRook(targetPosition, false)
 		case "b":
-			err = b.moveBishop(position[1:3], false)
+			err = b.moveBishop(targetPosition, false)
 		case "n":
-			err = b.moveKnight(position[1:3])
+			err = b.moveKnight(targetPosition)
 		case "q":
-			err = b.moveQueen(position[1:3])
+			err = b.moveQueen(targetPosition)
 		case "k":
-			err = b.moveKing(position[1:3])
+			err = b.moveKing(targetPosition)
 		default:
-			err = fmt.Errorf("invalid move: %s", position)
+			err = fmt.Errorf("invalid move %s: %v", move, err)
 		}
 	} else {
-		return fmt.Errorf("invalid move: %s", position)
+		return fmt.Errorf("invalid move %s: %v", move, err)
 	}
 
 	if err != nil {
@@ -341,7 +355,7 @@ func (b *Board) Move(position string) error {
 		b.turn = Light
 	}
 
-	b.moves = append(b.moves, position)
+	b.moves = append(b.moves, move)
 
 	return nil
 }
@@ -752,6 +766,30 @@ func (b *Board) getPiece(x int, y int) *Piece {
 	return b.tiles[x][y]
 }
 
+func (b *Board) getCollision(position string) (*Piece, error) {
+	var (
+		x, y      int
+		p         *Piece
+		collision bool
+		err       error
+	)
+	if x, y, err = getXY(position); err != nil {
+		return nil, err
+	}
+
+	p = b.getPiece(x, y)
+
+	// check if position is occupied by own piece
+	collision = p != nil && p.Color == b.turn
+	if collision {
+		return p, nil
+	}
+
+	// TODO: check if path is blocked by some piece
+
+	return nil, nil
+}
+
 func getTileColor(x, y int) Color {
 	if x%2 == y%2 {
 		return Light
diff --git a/chess/board_test.go b/chess/board_test.go
index 0858521..aff03d2 100644
--- a/chess/board_test.go
+++ b/chess/board_test.go
@@ -120,6 +120,26 @@ func TestBoardMoveKnight(t *testing.T) {
 	assertNoPiece(t, b, "g8")
 }
 
+func TestBoardMoveKnightInvalid(t *testing.T) {
+	b := chess.NewBoard()
+
+	// out of reach
+	assertMoveError(t, b, "Ng3", "no knight found that can move to g3")
+	assertMoveError(t, b, "Nb3", "no knight found that can move to b3")
+
+	// blocked by own piece
+	assertMoveError(t, b, "Nd2", "d2 blocked by white pawn")
+	assertMoveError(t, b, "Ne2", "e2 blocked by white pawn")
+
+	b.Move("Nf3")
+
+	assertMoveError(t, b, "Ng6", "no knight found that can move to g6")
+	assertMoveError(t, b, "Nb6", "no knight found that can move to b6")
+
+	assertMoveError(t, b, "Ne7", "e7 blocked by black pawn")
+	assertMoveError(t, b, "Nd7", "d7 blocked by black pawn")
+}
+
 func TestBoardMoveBishop(t *testing.T) {
 	b := chess.NewBoard()
 
diff --git a/chess/piece.go b/chess/piece.go
index d3ce93b..f932a44 100644
--- a/chess/piece.go
+++ b/chess/piece.go
@@ -16,6 +16,34 @@ type Piece struct {
 	Image image.Image
 }
 
+func (p *Piece) String() string {
+	n := ""
+	switch p.Name {
+	case Pawn:
+		n = "pawn"
+	case Knight:
+		n = "knight"
+	case Bishop:
+		n = "bishop"
+	case Rook:
+		n = "rook"
+	case Queen:
+		n = "queen"
+	case King:
+		n = "king"
+	}
+
+	c := ""
+	switch p.Color {
+	case Light:
+		c = "white"
+	case Dark:
+		c = "black"
+	}
+
+	return fmt.Sprintf("%s %s", c, n)
+}
+
 type PieceName string
 
 const (