The University of the Philippines Diliman (also referred to as UPD, UP Diliman, or simply UP) is a coeducational, research state university located in Diliman, Quezon City, Philippines. It was established on February 12, 1949 as the flagship campus and seat of administration of the University of the Philippines System, the national university of the Philippines. UP Diliman is the fourth oldest constituent university of UP. It has consistently ranked first in government-backed polls on the most significant higher education school in the entire Philippines. It has been ranked between the 60-75 bracket in the best universities in Asia list

It is the largest constituent university in the University of the Philippines System in terms of number of degree-granting academic units, student population, faculty, and library resources.[5] There are 27 degree-granting units on campus, accounting for 22,031[6] students of which, 15,299 are undergraduates. UP Diliman had a complement of 1,526 full-time faculty in 2012, of whom 528 have doctoral degrees.[6]

In addition to the units in the main campus, UP Diliman has extension programs in Angeles City (the Clark Freeport Zone area) and Olongapo City as well as a marine laboratory in Bolinao, Pangasinan under The Marine Science Institute,[7] and an annex campus at Bonifacio Global City, a financial district in the city of Taguig.[8] UP Diliman offers academic programs in 247 major fields.[6] There were 70 programs at the undergraduate level, 109 at the master’s level and 68 at the doctoral level.[6]

The UP Diliman campus is also the site of the country's National Science Complex. Notable research units of UP Diliman centered at the National Science Complex include the Marine Science Institute (MSI), the National Institute of Geological Sciences (NIGS), the National Institute of Physics (NIP), the National Institute of Molecular Biology and Biotechnology-Diliman (NIMBB-Diliman), and the National Institute for Science and Mathematics Education Development (NISMED), which are all pioneers of scientific research and development in the Philippines.[3] The Sentro ng Wikang Filipino-Diliman is devoted to research on the intellectualization of the Filipino language.