Alcázar de San Juan (often called simply Alcázar or Alcázar de Consuegra) is a town and municipality in the province of Ciudad Real, part of the autonomous community of Castile-La Mancha, Spain. It is located in the plain of La Mancha.

Its name is taken from an old moorish fortress (al-qaSsr in Arabic language), which was afterwards garrisoned by the knights of St John (San Juan in Spanish language).

Much of the action of Cervantes' Don Quixote takes place around Alcázar. The village of El Toboso was the home of the Lady Dulcinea del Toboso; Argamasilla de Alba is declared by tradition to be the birthplace of the original of Don Quixote himself.

Alcázar de San Juan was a main railway hub.