San Diego State University (SDSU, San Diego State) is a public research university in San Diego, California, and is the largest and oldest higher education institution in San Diego County. Founded in 1897 as San Diego Normal School, it is the third-oldest university in the 23-member California State University (CSU). SDSU has a student body of more than 35,000 and an alumni base of more than 280,000.

The Carnegie Foundation has designated San Diego State University a "Research University with high research activity," placing it among the top 200 higher education institutions in the country conducting research. In the 2009–10 academic year, the university obtained $150 million for research, including $26 million from the National Institutes of Health. The university soon expects to be classified as "Doctoral/Research-Extensive". As reported by the Faculty Scholarly Productivity Index (FSP Index) released by the Academic Analytics organization of Stony Brook, New York, SDSU is the number one small research university in the United States for four academic years in a row. SDSU sponsors the second highest number of Fulbright Scholars in the state of California, just behind UC Berkeley. Since 2005, the university has produced over 65 Fulbright student scholars.

SDSU is an acronym that may refer to: