G4S plc (formerly Group 4 Securicor) (LSE: GFS, OMX: G4S) is a global security services company headquartered in Crawley, United Kingdom. It is the world's largest security company measured by revenues and has operations in more than 110 countries. With over 585,000 employees it is the world's second largest private sector employer (after Wal-Mart).
Its primary listing is on the London Stock Exchange and it is a constituent of the FTSE 100 Index. It has a secondary listing on the Copenhagen Stock Exchange.
The company has its origins in a guarding business founded in Copenhagen in 1901 by Marius Hogrefe originally known as Kjøbenhavn Frederiksberg Nattevagt and subsequently renamed Falck.