The City of London Sinfonia (CLS) is an English chamber orchestra based in London. In London, the CLS performs regularly at Cadogan Hall and St Paul's Cathedral. It is also the resident orchestra at Opera Holland Park. The CLS has annual residencies in four towns in Southern England: Ipswich, King's Lynn, High Wycombe and Chatham. It records regularly and makes an overseas tour every year. The CLS performs chamber orchestra and ensemble repertoire from the Baroque period to the present day, and has a particular reputation for its programming focus on the human voice.

Richard Hickox founded the CLS in 1971 and remained its music director and artistic director until his death in November 2008. Past principal guest conductors have included Marin Alsop and Douglas Boyd. In November 2009, the CLS announced the appointment of Stephen Layton as its second Artistic Director, effective with the 2010-2011 season, for an initial contract of 3 years. Layton is also to have the title of Principal Conductor. Simultaneously, the CLS announced the appointment of clarinetist Michael Collins also as Principal Conductor, effective in September 2010, for an initial period of 3 years.