The London Sinfonietta is an English contemporary chamber orchestra founded in 1968 and based in London.

The London Sinfonietta’s mission is to place the best contemporary classical music at the heart of today’s culture; engaging and challenging the public through inspiring performances of the highest standard, and taking risks to develop new work and talent.

The ensemble has headquarters at Kings Place and is Resident Orchestra at the Southbank Centre; it continues to take the best contemporary music to venues and festivals across the UK and worldwide with a busy touring schedule. Since its inaugural concert in 1968—giving the world premiere of Sir John Tavener’s The Whale—the London Sinfonietta’s commitment to making new music has seen it commission over 300 works, and premiere many hundreds more.

The core of the London Sinfonietta is its 18 Principal Players, representing some of the best solo and ensemble musicians in the world. In September 2013 the ensemble launched its Emerging Artists Programme, which gives brilliant professional musicians at the start of their careers the opportunity to work alongside those Principal Players on stage across the season.

The London Sinfonietta’s recordings comprise a catalogue of 20th-century classics, on numerous prestigious labels as well as the ensemble's own London Sinfonietta Label.