WIYN Telescope, Modern optical telescope at Kitt Peak National Observatory, Arizona, United States

The WIYN Telescope is a 3.5-meter Ritchey–Chrétien telescope on an altitude-azimuth mount at Kitt Peak National Observatory in Arizona, the site's second-largest optical telescope. Its lightweight borosilicate primary mirror, 3.49885 m across, was made at the Richard F. Caris Mirror Lab and rests on 66 active-optics actuators. The telescope sits in a half-rhombicuboctahedron dome.

The WIYN Consortium, formed by the University of Wisconsin–Madison, Indiana University and Yale University, funded most of the capital costs, with NOAO providing operating services. Yale withdrew on 1 April 2014 and the University of Missouri replaced it that autumn; in 2015 the NASA–NSF NN-EXPLORE partnership took over NOAO's share, though NOAO still manages operations. Directors included George Jacoby (2000–2008), Pierre Martin (2008–2010) and, from 2013, interim director Eric Hooper.

The name NEID comes from the Tohono Oʼodham word for "to see", a nod to the Indigenous people of the region around Kitt Peak. The spectrograph, built at Pennsylvania State University from 2016, finished commissioning on 2 June 2021 and measures stellar radial velocities to about 50 cm/s. Hydra, in service since 1990, can observe up to 100 objects at once.

The WIYN telescope sits on Kitt Peak, southwest of Tucson, Arizona, and is a working research facility rather than a visitor attraction. Its 3.5 m mirror is housed in a half-rhombicuboctahedron dome, and observing time is allocated to the WIYN Consortium partners and their collaborators. Access to the telescope and dome is arranged through the consortium, not through public tours.

A specialized instrument at this telescope was designed to search for distant planets by detecting subtle movements in stars caused by orbiting worlds. This technique has helped astronomers discover numerous worlds beyond our solar system.