Oregon State University (OSU) is a public land-grant research university in Corvallis, Oregon, United States. OSU offers more than 200 undergraduate degree programs, and graduate and doctorate degrees through all 11 colleges. The university is classified among "R1: Doctoral Universities – Very high research activity". It has the seventh-largest engineering college in the nation (2023). Undergraduate enrollment for all colleges combined averages over 32,000 while an additional 5,000 students are engaged in post-graduate coursework through the university.

In 2024, nearly 38,000 students were enrolled at OSU, making it the largest university in the state. Out-of-state students typically make up over one-quarter of the student body. Since its founding, over 272,000 students have graduated from OSU.

Initially chartered as a land-grant university, OSU became one of only four inaugural members of the sea grant program in 1971. Membership in the Space Grant came in 1991, followed by Sun Grant membership in 2003. Only three schools in the nation held memberships in all four research areas at this time, a distinction that has helped OSU become a leading research university today. OSU received a record high $449.9 million in research funding for the 2022 fiscal year and has ranked as the state's top earner in research funding for over 50 years. OSU is also one of the top five doctoral university destinations in the nation for Fulbright Scholars (2022–2023).

The university's roots date to 1856, when it was founded as a primary and preparatory community school known as Corvallis Academy. Corvallis area Freemasons played a leading role in developing the academy. Several of the university's largest buildings are named after these founders today. The early academy is recognized as the first to offer a postsecondary public education in the Oregon Territory. The first administrator and teacher was John Wesley Johnson, a famous figure in Oregon higher education. Johnson received his secondary education in Corvallis and his undergraduate from Pacific University before managing the new academy. He later attended Yale University and became an instrumental figure in the development and administration of several other early Oregon colleges. Between 1860 and 1868, the Southern Methodist Church took ownership and ran the academy privately. In 1865, William A. Finley was hired as president and expanded the curriculum to include upper-level courses. The growth in curriculum made OSU a magnet for many Northwest young adults seeking professions.

On August 22, 1868, the official articles of incorporation were filed for Oregon State University, known then as Corvallis College. To help ensure the state's sole public college would be well funded, the Oregon Legislative Assembly designated it Oregon's Land-grant university and the "agricultural college of the state of Oregon". Two months later, on October 27, 1868, OSU was chartered as the state's first and only public college. Finley remained in his post and is recognized as OSU's first president. Although OSU officially became a fully public, non-denominational institution in 1868, the Southern Methodist Church remained an important part of the school's administration through the mid-1880s. Up until the turn of the 20th century, the early college adopted seven name variations. As with many land-grant colleges, name changes were common during this period, and helped schools align with the largest federal grants in agricultural research. The Morrill Land-Grant Acts were pivotal in helping OSU and other early American land-grant universities survive and thrive during a time when traditional colleges and universities often faced financial hardship. "This dependable flow of funds provided the long-sought financial foundation the colleges needed and encouraged state governments to make annual appropriations as well."

Acceptance of the federal grant required the college to comply with many new requirements. The school was then authorized to grant Bachelor of Arts, Bachelor of Science and Master of Arts degrees. OSU's land-grant designation did not go without contention. In its early development, the cash-strapped founders of the University of Oregon asked the state to designate their planned institution Oregon's land-grant university, but the request was denied. The first graduates received a Bachelor of Arts degree in 1870. Within two years, the school was renamed Corvallis State Agricultural College. As the school's name changed, so did its mission. Science and technology coursework became the most popular majors starting in 1900.

In 1914, the Oregon State Board of Higher Education, known then as the State Board of Higher Curricula, began assigning specific colleges to Oregon State University and the University of Oregon in an effort to eliminate duplication. "...the board confined studies in engineering and commerce to the Corvallis campus and major work in the liberal arts and related subjects to the University of Oregon in Eugene. This was the first in a series of actions to make the curricula of the two schools separate and distinct."

In 1927, the school's name was officially changed from Oregon Agricultural College to Oregon State Agricultural College (OSAC).