Serco is a multinational outsourcing company that provides outsourced public services and security services. In the UK, Serco operates in a number sectors of public service provision:

• Health services, including NHS and GP services
• Transport, including train services on Merseyside and the north of England, in partnership with Abellio
• Prisons and justice, where it was banned from further government contracts after overcharging on electronic tagging contracts
• Immigration and border control, including the infamous Yarl's Wood detention centre
• Defence, mainly maintenance contracts.​
• Shared and back-office services for local councils

Serco is a UK-based plc that is listed on the London Stock Exchange.

Serco was forced to pull out of a contract to provide out-of-hours GP services in Cornwall after it emerged that the company had been falsifying data and that it had a ‘bullying culture' which discouraged whistleblowing in the interests of patients.