升变是国际象棋中的一种特殊着法，指兵到达最底一横行时，可变成后、车、马、象的其中一种。在一些变体中，容许变成王甚至是对方的棋子。

由于后在棋子中威力最强，故兵升变成后最为常见，称为「变后」（Queening）。兵变为其他子的升变称为「低升变」（Underpromotion），多数只于棋局问题中出现。

因后兼具车、象的功能而不具备马的功能，故兵升变为马有时能发挥特别作用，尤其升变之后可以将军。有时候，升变为车是为避免对方无子可动而被逼和。现实棋局中，升变为象十分罕见，大约33000局之中只有1局。

截至2006年，包含3,200,000棋局（大部分是国际大师的对赛）的ChessBase数据库中约1.5%的棋局有升变一着。在这些升变当中（把同一棋手升变成同一子的所有棋局视为一局），升变的比例大约是：

Promotion is a chess rule that a pawn that reaches its eighth rank is immediately changed into the player's choice of a queen, knight, rook, or bishop of the same color. The new piece replaces the pawn on the same square, as part of the same move. The choice of new piece is not limited to pieces that have already been captured; it is legal for promotion to result in a player controlling, for example, two Queens of the same color despite starting the game with one. Promotion is immediate and mandatory for any pawn that reaches its eighth rank, and the pawn may not remain a pawn. Pawn promotion, or the threat of it, often decides the result of a chess endgame.