The London Sinfonietta is among the leading ensembles in the U.K. devoted largely to contemporary music. It is a chamber-sized orchestra, consisting of about 17 members, with a single player each on violin I, violin II, and the other major instruments of the orchestra, including percussion and electronics. The LS has commissioned and performed more than 200 new works over the years, and premiered countless others. The programs feature works by such well-known contemporary composers as Berio, Birtwistle, Boulez, Nono, Reich, and Stockhausen, as well as lesser known figures like Anna Meredith, Claudia Molitor, Tansy Davies, and Larry Goves. But the LS also performs more mainstream repertory, including works by J.S. Bach, Stravinsky, Britten, and even Broadway fare by Jerome Kern and Cole Porter, as well as jazz works. The orchestra is one of several resident ensembles at London's Southbank Centre and makes regular tours throughout Europe, Asia, and the Americas. The LS has made countless recordings over the years, many available from EMI, Decca, and DG.

The London Sinfonietta was founded in 1968 by Nicholas Snowman and David Atherton, the latter serving as music director until 1973. Since stepping down Atherton has regularly led the orchestra in concert and made many acclaimed recordings, among them the highly praised 1980 Chandos recording of Tippett's opera King Priam.

Apart from Atherton and composer/conductor Oliver Knussen, who served as music director from 1998-2002, the LS has generally been led by guest conductors over the years who typically are engaged to conduct a series of concerts.

Artistic directors have overseen much of the orchestra's activities. Michael Vyner was perhaps the ensemble's most cherished artistic director, serving from 1972 until his death in 1989. The LS performed many new works written as tributes to Vyner after his passing, including Peter Maxwell Davies' Threnody on a Plainsong for Michael Vyner.

Pianist Paul Crossley served as artistic director until 1994. German conductor Markus Stenz led the orchestra in many concerts from 1994-1998. Though Knussen stepped down as music director in 2002, he began serving as conductor laureate upon his departure and still regularly conducts the orchestra. Though most regular-season concerts by the LS are given in Southbank Centre, since 2008 a small portion are presented in Kings Place, Kings Cross in London. Among the more acclaimed later recordings of the LS is the 2006 CD on Explore Records of Hans Werner Henze's Voices, led by the composer., Rovi