The biretta is a square cap with three or four ridges or peaks, sometimes surmounted by a tuft, traditionally worn by Roman Catholic clergy and some Anglican and Lutheran clergy. It is also the term used for a similar cap worn by those holding doctoral degrees from some universities, and is occasionally used for caps worn by advocates in law courts, for instance the Advocates in the Channel Islands.

Its origins are uncertain but is mentioned as early as the tenth century. The most probable origin of the biretta is the academic hat of the high Middle Ages, which was a soft, square cap. The medieval academic hat is also the ancestor of the modern mortarboard hat used today in secular universities. The tuft or pom sometimes seen on the biretta was added later; the earliest forms of the biretta did not bear the device.

The biretta is used by all ranks of the clergy from cardinals to priests, deacons and seminarians. Those worn by cardinals are scarlet red. After the Second Vatican Council the ceremony of giving the galero to Cardinals was replaced with giving the biretta. The biretta of a bishop is amaranth (purple), while those worn by priests, deacons, and seminarians are black. The Pope does not make use of the biretta, instead wearing the more ancient camauro, which Pope Benedict XVI has brought back into use.

The liturgical biretta has three peaks, with the 'peak-less' corner worn on the left side of the head.  An academic Biretta has four peaks.