G4S plc (formerly Group 4 Securicor) is a British multinational security services company headquartered in Crawley, England.
The company was set up in 2004 when London-based company Securicor amalgamated with Danish business Group 4 Falck. The company offers a range of services, including the supply of security personnel, monitoring equipment, response units and secure prisoner transportation. G4S also works with governments overseas to deliver security.
It is the world's largest security company measured by revenues and has operations in around 125 countries. With 618,000 employees, it is world's third-largest private employer, the largest European and African private employer, and among the largest on the London Stock Exchange. G4S was founded in 2004 by the merger of the UK-based Securicor plc with the Denmark-based Group 4 Falck.
G4S has a primary listing on the London Stock Exchange and is a constituent of the FTSE 250 Index, having been relegated from the FTSE 100 Index in December 2015. (Source: Wikipedia)