The Nancy Grace Roman Space Telescope (shortened as Roman or the Roman Space Telescope, and formerly the Wide-Field Infrared Survey Telescope or WFIRST) is a NASA infrared space telescope currently in development. Roman was recommended in 2010 by the United States National Research Council Decadal Survey committee as the top priority for the next decade of astronomy. On 17 February 2016, WFIRST was approved for development and launch.

The Roman Space Telescope is based on an existing 2.4 m wide field of view primary mirror and will carry two scientific instruments. The Wide-Field Instrument (WFI) is a 300.8-megapixel multi-band visible and near-infrared camera, providing a sharpness of images comparable to that achieved by the Hubble Space Telescope (HST) over a 0.28 square degree field of view, 100 times larger than imaging cameras on HST. The Coronagraphic Instrument (CGI) is a high-contrast, small field of view camera and spectrometer covering visible and near-infrared wavelengths using novel starlight-suppression technology.

The design of the Roman Space Telescope has heritage to various proposed designs for the Joint Dark Energy Mission (JDEM) between NASA and the Department of Energy (DOE). Roman adds some extra capabilities to the original JDEM proposals, including a search for extra-solar planets using gravitational microlensing. In its present incarnation (2015), a large fraction of its primary mission will be focused on probing the expansion history of the Universe and the growth of cosmic structure with multiple methods in overlapping redshift ranges, with the goal of precisely measuring the effects of dark energy, the consistency of general relativity, and the curvature of spacetime.

In 2018 and 2020, there were attempts by the Trump administration and NASA to reduce or terminate the budget for the WFIRST, in part because of cost overruns of the James Webb Space Telescope. However, Congress included some funding. On 2 March 2020, NASA announced that it had approved WFIRST to proceed to implementation, with an expected development cost of US$3.2 billion and a maximum total cost of US$3.934 billion, including the coronagraph and five years of mission science operations.

On 20 May 2020, NASA Administrator Jim Bridenstine announced that the mission would be named the Nancy Grace Roman Space Telescope in recognition of the former NASA Chief of Astronomy's foundational role in the field of space astronomy.

On 31 March 2021, the NASA Office of Inspector General (OIG) released a report that stated that the development of the Nancy Grace Roman Space Telescope had been affected by the COVID-19 pandemic, which hit the US during a particularly important time in the telescope's development. NASA is expecting a total impact of US$400 million due to the pandemic and its effect on sub-contractors for the project. On 29 September 2021, NASA announced that Roman had passed its Critical Design Review (CDR), and that with predicted impacts from COVID-19 disruptions the launch date would be no later than May 2027.