Royal Air Force Menwith Hill (RAF Menwith Hill) is a Royal Air Force station near Harrogate, North Yorkshire, England, which provides communications and intelligence support services to the United Kingdom and the United States. The site contains an extensive satellite ground station and is a communications intercept and missile warning site. It has been described as the largest electronic monitoring station in the world.

RAF Menwith Hill is owned by the Ministry of Defence (MoD), but made available to the US Department of Defense (DoD) under the NATO Status of Forces Agreement 1951 and other, undisclosed agreements between the US and British governments. His Majesty's Government (HMG) is entitled to possession of the site and retains control over its use and its facilities, though the administration of the base is the responsibility of the US authorities, with support provided by around 400 staff from Government Communications Headquarters (GCHQ), in addition to United States Air Force (USAF) and US National Security Agency (NSA) personnel. In 2014, the number of American personnel was reduced as part of a streamlining of operations due to improvements in technology.

The site acts as a ground station for a number of satellites operated by the US National Reconnaissance Office, on behalf of the NSA, with antennas contained in numerous distinctive white radomes, locally referred to as "the golf balls", and is alleged to be an element of the ECHELON system.

The site is one of three main sites operated by the United States across the globe as a major satellite monitoring station and intelligence gathering location. The other two sites are located in America and Australia, having similar roles and working together with RAF Menwith Hill to develop knowledge around American, British and Australian interests. The Australian site is known as the Joint Defence Facility Pine Gap.

In 1954, the British War Office purchased 246 acres (100 hectares) of land at Nessfield Farm, located approximately 7 kilometres (4.3 mi) west of Harrogate, North Yorkshire. The area purchased soon increased to 562 acres (227 hectares) and were made available by the British Government to the United States Department of Defense. The site was considered by the US as suitable for gathering signals intelligence from the northern parts of Western Europe and Eastern Europe, specifically the Soviet Union and its associated Warsaw Pact countries. The Yorkshire Dales' low level of background radio noise made it an especially good location for the task. The UK provided assurances to the US that the site would be available to them for at least 21 years.

Construction of the station on behalf of the United States Army Security Agency (USASA) began in April 1956. Building costs at the time were $6.8 million as well as a further $1.2 million for personnel housing. Initially named Field Station 8613, the site was renamed 13th USASA Field Station on 1 January 1957 and again renamed on 1 January 1959, as Menwith Hill Station. Due to adverse ground conditions and weather, there were delays to the construction programme, with the station finally becoming operational during June 1959.

Operationally, Menwith Hill was assigned to the USASA Headquarters in Frankfurt, West Germany, whereas for logistical support it was attached to the US Air Force's Third Air Force, which at the time had its headquarters in the UK. Security at the station was provided by a US Army military police detachment and the British Air Ministry Constabulary. However, if the site was compromised during an invasion, three earth-covered bunkers contained ammunition and thermite charges which could be used to destroy classified equipment and material.

The station initially comprised a headquarters building, barracks, dependent housing and support facilities such as a cinema and social clubs. The operations building was located inside a secure compound, within a large antenna field, approximately 1.6 kilometres (0.99 mi) from the main site. It was equipped with large high frequency (HF) directional rhombic antennas that could detect signals from around the globe. Over two-hundred Collins R-390A HF communications receivers were used to collect a vast range of signal in the HF band, including carrier waves, voice signals, and burst transmissions. Within the operations centre was the communications centre which was staffed by cryptographers using deciphering equipment, however a large amount of the signals collected were encrypted before being forwarded for processing to the US National Security Agency's Fort Meade facility in Maryland.