San Diego State University (SDSU) is a public research university in San Diego, California, United States. Founded in 1897, it is the third-oldest university and southernmost in the 23-member California State University (CSU) system. SDSU is the oldest higher education institution in San Diego; its academic roots were established as a normal school in University Heights, then known as the San Diego Normal School. In the fall of 2025, the university enrolled a record 41,184 students.

SDSU comprises eight colleges and offers over 200 degree programs at the undergraduate and graduate levels. It is accredited by the WASC Senior College and University Commission (WSCUC). The university is classified among "R1: Doctoral Universities – Very high research activity". It is a federally-designated Hispanic-Serving Institution (HSI) as well as an Asian American and Native American Pacific Islander-Serving Institution (AANAPISI).

SDSU's athletic teams compete as the San Diego State Aztecs; the Aztecs nickname was chosen by students in 1925. They compete in National Collegiate Athletic Association (NCAA) Division I, primarily as a member of the Mountain West Conference (Pac-12 Conference starting in 2026). SDSU currently fields varsity teams across 17 NCAA-sanctioned sports. As of 2021, athletes from the university had won 14 medals at the Olympic Games.