A midfielder is an outfield position in association football. Midfielders may play an exclusively right back role, breaking up attacks, and are in that case known as defensive midfielders. As central midfielders often go across boundaries, with mobility and passing ability, they are often referred to as deep-lying midfielders, play-makers, box-to-box midfielders, or holding midfielders. There are also attacking midfielders with limited defensive assignments.

The size of midfield units on a team and their assigned roles depend on what formation is used; the unit of these players on the pitch is commonly referred to as the midfield. Its name derives from the fact that midfield units typically make up the in-between units to the defensive units and forward units of a formation.

Managers frequently assign one or more midfielders to disrupt the opposing team's attacks, while others may be tasked with creating goals, or have equal responsibilities between attack and defence. Midfielders are the players who typically travel the greatest distance during a match. Midfielders arguably have the most possession during a game, and thus they are some of the fittest players on the pitch. Midfielders are often assigned the task of assisting forwards to create scoring chances.