Colorado State University (Colorado State or CSU) is a public land-grant research university in Fort Collins, Colorado. It is the flagship university of the Colorado State University System. Colorado State University is classified among "R1: Doctoral Universities – Very high research activity". It was founded in 1870 as Colorado Agricultural College and in 1935 was renamed the Colorado State College of Agriculture and Mechanic Arts. In 1957, the Colorado General Assembly approved its current name, Colorado State University.

In 2018, enrollment was approximately 34,166 students, including resident and non-resident instruction students. The university has approximately 2,000 faculty in eight colleges and 55 academic departments. Bachelor's degrees are offered in 65 fields of study, with master's degrees in 55 fields. Colorado State confers doctoral degrees in 40 fields of study, in addition to a professional degree in veterinary medicine. CSU's campus boasts the Engines and Energy Conversion Laboratory (EECL), the University Center for the Arts, which houses the Avenir Museum of Design and Merchandising and the Gregory Allicar Museum of Art, the James L. Voss Veterinary Teaching Hospital, and the Cooperative Institute for Research in the Atmosphere (CIRA).

In fiscal year 2018, CSU spent $375 million on research and development, ranking 65th in the nation overall and 39th when excluding medical school spending. CSU graduates include Pulitzer Prize winners, astronauts, CEOs, and two former governors of Colorado. In fiscal year 2021, CSU spent $447.2 million on research and development

The Colorado State Rams compete in the NCAA Division I Mountain West Conference. Swimmer and six-time Olympic gold medalist Amy Van Dyken is one of CSU's most notable athletes. The school renamed West Drive, which stretches along the west side of the Administration Building at the south end of CSU's Oval, Amy Van Dyken Way.