Cosette is a fictional character in the 1862 novel Les Misérables by Victor Hugo and in the many adaptations of the story for stage, film, and television. Her birth name, Euphrasie, is only mentioned briefly. As the orphaned child of an unmarried mother deserted by her father, Hugo never gives her a surname. In the course of the novel, she is mistakenly identified as Ursule, Lark, or Mademoiselle Lanoire.

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.