The Johannes Gutenberg University of Mainz is an institute of higher education in Mainz, Rhineland Palatinate, Germany. With approximately 35,000 students (2005) in about 150 schools and clinics, it is among the top ten largest universities in Germany. Starting on January 1, 2005, the university was reorganized into 11 faculties of study.

The first University of Mainz goes back to the Archbishop of Mainz, Prince-elector and Reichserzkanzler Adolf II von Nassau. At the time, establishing a university required papal approval and Adolf II initiated the approval process during his time in office. The university, however, was first opened in 1477 by Adolf's successor to the bishopric, Diether von Isenburg. In the confusion after the establishment of the Mainz Republic of 1792 and its subsequent recapture by the Prussians, academic activity came to a gradual standstill. In 1798 the university became active again under French governance, and lectures in the department of medicine took place until 1823.

The extant Johannes Gutenberg University of Mainz was founded in 1946 by the French occupying power. In a decree on March 1 the French military government implied that the University of Mainz would continue to exist: the University shall be "enabled to resume its function". The remains of Luftwaffe barracks erected in 1938 after the remilitarization of the Rhineland during the Third Reich served as the university's first buildings and are still in use today.