Promotion is the central goal of most pawn endgames. When a pawn reaches the last rank, it becomes a queen, rook, bishop, or knight. The typical choice is to promote to a queen, but underpromotion to a knight or rook is sometimes necessary for tactical reasons. Knight underpromotion can save a lost game by delivering check or, crucially, by giving checkmate when queen promotion would result in stalemate. Rook underpromotion is similarly used to avoid stalemate when a queen promotion would leave the opponent with no legal moves. The Saavedra position is a famous study illustrating this principle: a rook underpromotion, against all instinct, is the only winning move.
Stalemate occurs when a player has no legal move but is not in check, and it is a draw. This makes stalemate one of the most powerful defensive resources in losing positions. Common basic endgames illustrate the range of outcomes. The K vs K endgame is a trivial draw due to insufficient material. K+Q vs K is a routine win, achieved by boxing in the king. K+R vs K is a win but requires care to avoid stalemate. K+2B vs K and K+B+N vs K both win but demand precise technique; K+B+N mate requires the famous W-maneuver to drive the king to the correct corner, namely the corner matching the bishop's color. K+2N vs K is a draw with best play unless the opponent has pawns.
The K+P vs K endgame is the simplest material endgames, but its outcome depends entirely on key squares, opposition, and whose move it is. Zugzwang describes a position where any move worsens the player's situation, and in mutual zugzwang, both sides would lose if forced to move. Triangulation is the technique that creates zugzwang: by moving along a triangle and returning, a player loses a tempo and hands the move to the opponent. Deep zugzwang refers to positions requiring many moves to reach such a state. The principle of the lost tempo thus connects directly to triangulation and zugzwang, allowing the stronger side to make progress without directly advancing.