Serco Group plc is a British multinational defence, health, space, justice, migration, customer services, and transport company. It is headquartered in Hook, Hampshire, England. The company operates in continental Europe, the Middle East, the Asia Pacific region, including Australia and Hong Kong, and North America. It is listed on the London Stock Exchange and is a constituent of the FTSE 250 Index.

The company was founded as RCA Services Limited in 1929, a UK-based division of the Radio Corporation of America. The company began providing technical and engineering services to the British War Office during the Second World War. During the Cold War era, it specialised in the provision of defense systems engineering and facilities management services, including the maintenance of sonar, early warning radar and satellite systems. Following a management buyout, the firm changed to the name Serco ('Services Company') in 1987 and was listed on the London Stock Exchange one year later. The company was restructured during the 1980s, reorientated itself towards services beyond engineering, and expanded its presence globally.

Serco has encountered controversy, described by legal services firm Appleby as a "history of problems, failures, fatal errors and overcharging". During 2013, then-chairman Alastair Lyons resigned from the company after it was found that it had overcharged the UK Government for electronically monitoring criminals. Serco underwent a corporate renewal programme during the 2010s, created in collaboration with the United Kingdom government, which overhauled the management of contracts and commercial auditing.

Serco was founded in 1929 as RCA Services Limited, a British-based division of the Radio Corporation of America, and initially provided technical services to the cinema industry.

RCA Services Limited began providing services to government departments during the Second World War. After the onset of the conflict, the company was contracted by the British War Office due to the company's engineering and technical background to supply the department with equipment which would simulate the sound of warfare to confuse the enemy. During 1952, RCA Services was contracted to produce submarine-detecting sonar equipment for the United States Navy. In 1960, it was awarded the contract to design, install, and maintain the UK Ministry of Defence (MoD) Ballistic Missile Early Warning System, including ongoing facility management such as cleaning, transport, and logistical stores.

In the 1980s, the European Space Agency contracted RCA Services to support and maintain computer systems and satellites.

By the 1980s, RCA Services began to interpret their company product as the management, rather than being just an engineering and science company. For their MoD Radar contract at RAF Fylingdales, "the art, it turned out, was in running the people, not the radar." During 1984, RCA Services was awarded the Ministry of Defence's first outsourcing contract, under which it managed warehousing using the knowledge of staff who had completed similar work at RAF Fylingdales.

Following the takeover of RCA by General Electric in late 1985, RCA Services Limited was bought out by its local management. During 1987, the firm changed its name to Serco ('Services Company') and became a London Stock Exchange listed company one year later. By 1990s, Serco had expanded from the United Kingdom and Europe, developing a global presence with major activities in Hong Kong, Australia, New Zealand, and North America.