Les Misérables, colloquially known as Les Mis or Les Miz, is a sung-through musical with music by Claude-Michel Schönberg, lyrics by Alain Boublil and Jean-Marc Natel, and a book by Schönberg and Boublil, based on the 1862 novel of the same name by Victor Hugo. The original French musical premiered in Paris in 1980 with direction by Robert Hossein. Its English-language adaptation, with lyrics by Herbert Kretzmer, produced by Cameron Mackintosh, has been running in London since October 1985, making it the longest-running musical in the West End and the second longest-running musical in the world after the original Off-Broadway run of The Fantasticks. A film adaptation was released in 2012.

Musical theatre is a form of theatrical performance that combines songs, spoken dialogue, acting and dance. The story and emotional content of a musical – humor, pathos, love, anger – are communicated through words, music, movement and technical aspects of the entertainment as an integrated whole. Although musical theatre overlaps with other theatrical forms like opera and dance, it may be distinguished by the equal importance given to the music as compared with the dialogue, movement and other elements. Since the early 20th century, musical theatre stage works have generally been called, simply, musicals.