The endgame is the final phase of a chess game, reached when most pieces have been exchanged and only a few remain on the board. Because endgames occur frequently at every level of play and frequently decide the outcome of games, studying them is essential. The principles learned in endgame study also illuminate decisions made earlier in the middlegame, since the player who understands the ending often makes better choices in earlier phases.
The single most important skill in endgames is king activity. Unlike the opening and middlegame, where the king hides for safety, in the endgame the king becomes an active attacker. A centralized king functions as the equivalent of a minor piece, and is often the decisive factor. The principle of moving the worst-placed piece first applies strongly here: rather than focusing on already-active pieces, players should improve their least effective unit, often the king itself. Other guiding principles include trading pieces when ahead to simplify into a winning position, and trading pawns when behind to reduce the position toward a defensible material balance.
The rule of two weaknesses states that a single weakness in one's position can usually be defended, but two cannot; the attacker therefore often needs to create multiple targets. Pawn structure plays an enormous role in determining plans: weak pawns (isolated, doubled, backward, or hanging) become targets, while a pawn majority on one wing can be converted into a passed pawn. Patience, calculation, and the wisdom to recognize when resignation is appropriate all complete the foundation of strong endgame play.