An infielder is a baseball player who plays on the infield, the dirt portion of a baseball diamond between first base and third base. The infield defensive positions are first baseman, second baseman, shortstop and third baseman. Pitchers and catchers are often considered distinct from infielders even though they play on the infield; they are sometimes described jointly as the battery.

Utility infielders are bench players who can play at least two infield positions. They are often weak hitters but skilled fielders, who enter the game in the late innings as defensive substitutes.

Among infielders, shortstops are generally the best fielders, followed by second basemen, third basemen, and first basemen, respectively. Conversely, more first and third basemen are good hitters than second basemen and shortstops. Second basemen and shortstops are referred to as "Middle Infielders," while third basemen and shortstops are called "Corner Infielders", or simply the "corners".