The California State University is a public university system in California, and the largest public university system in the United States. It consists of 23 campuses and seven off-campus centers, which together enroll 457,992 students and employ 56,256 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.

A university system is a set of multiple affiliated universities and colleges that are usually geographically distributed. Typically, all member universities in a university system share a common component among all of their various names. Usually, all member universities of a university system are governed by a system-wide governing body, such as a board of trustees or a board of regents. In the United States, many states have one or two state university systems under which many of their publicly funded universities are aligned, both in name and in governance. Additionally, for-profit universities, such as DeVry University, often have multiple campuses which share the same name; these may be, but are not always, described as a university system.