The California State University (Cal State or CSU) is a public university system in California, and the largest public university system in the United States. It consists of 22 campuses and seven off-campus centers, which together enroll 461,612 students and employ 63,375 faculty and staff members. In California, it is one of the three public higher education systems, along with the University of California and the California Community Colleges systems. The CSU system is officially incorporated as The Trustees of the California State University, and is headquartered in Long Beach, California.

Established in 1960 as part of the California Master Plan for Higher Education, the CSU system has its roots in the California State Normal Schools that were chartered in 1857. It holds the distinction of being the leading producer of bachelor's degrees in the country, with over 110,000 graduates each year. Additionally, the CSU system contributes to the state's economy by sustaining more than 209,000 jobs.

In the 2015–16 academic year, CSU awarded 52% of newly issued California teaching credentials, 33% of the state's information technology bachelor's degrees, and it had more graduates in business, criminal justice, engineering, public administration, and agriculture than all other colleges and universities in California combined. Altogether, about half of the bachelor's degrees, one-fourth of the master's degrees, and 3% of the doctoral degrees awarded annually in California are from the CSU. Additionally, 62% of all bachelor's degrees granted to Hispanic students in California and over half of bachelor's degrees earned by California's Latino, African American and Native American students combined are conferred by the CSU.

Since 1961, over four million alumni have received a degree from the CSU system. CSU offers more than 1,800 degree programs in some 240 subject areas. In fall of 2024, 11,135 (or 40%) of CSU's 27,505 faculty were tenured or on the tenure track.

Today's California State University system is the direct descendant of the Minns Evening Normal School, founded in 1857 by George W. Minns in San Francisco. It was a normal school, an institution that educated future teachers in association with the high school system and the first of its kind in California.

The school was taken over by the state in 1862 and moved to San Jose and renamed the California State Normal School; it eventually evolved into San Jose State University. A southern branch of the California State Normal School was created in Los Angeles in 1882. In 1887, the California State Legislature dropped the word California from the name of the San Jose and Los Angeles schools, renaming them State Normal Schools.

Later, other state normal schools were founded at Chico (1887) and San Diego (1897); they did not form a system in the modern sense, in that each normal school had its own board of trustees and all were governed independently from one another. By the end of the 19th century, the State Normal School in San Jose was graduating roughly 130 teachers a year and was "one of the best known normal schools in the West."

In 1919, the State Normal School at Los Angeles became the Southern Branch of the University of California; in 1927, it became the University of California at Los Angeles.