This was Mozart's composition for a chamber ensemble (a string quartet with an added double-bass). It is probably one of his most popular pieces. Oddly enough, Mozart never published 'Eine Kleine Nachtmusik' in his lifetime. It was left up to his widow, Constanze, to sell it in a job lot of his music to a publisher in 1799, presumably to raise much needed cash. It saw public light of day only in 1827, some forty years after it was written.