public, coeducational institution of higher learning in Stillwater, Oklahoma, U.S., a part of Oklahoma's State System of Higher Education. The university also operates branch campuses in Okmulgee and Oklahoma City and is part of Oklahoma State University-Tulsa (formerly University Center at Tulsa). The Stillwater campus comprises colleges of agricultural sciences and natural resources, business administration, education, human environmental sciences, veterinary medicine, arts and sciences, and engineering, architecture, and technology. Many undergraduate, graduate, doctorate, and professional degree programs are offered. The Oklahoma City and Okmulgee campuses grant associate's degrees. The university also offers a two-year general education at its campus in Kameoka, near Kyōto, Japan. Research facilities include the Oklahoma Center for Integrated Design and Manufacturing, the Oklahoma Food and Agricultural Products Research and Technology Center, and the Center for Laser and Photonics Research. Total enrollment is more than 26,000.

The university was established in 1890 as a land-grant (land-grant college) institution under the provisions of the Morrill Act of 1862. Instruction began in 1891. The university was then known as Oklahoma Agricultural and Mechanical College; it became Oklahoma State University in 1957. The branch in Okmulgee was founded in 1946, the Oklahoma City branch in 1961. The university added the College of Osteopathic Medicine, located in Tulsa, in 1988.