This introduction presents an overview of the key concepts discussed in the subsequent chapters in this book. The book describes the business and production realities that surround and shape filmmakers' musical choices. It considers the potential for variation between a filmmaker's intention and a perceiver's interpretation, and indeed between the interpretations of different perceivers, in regard to uses of pre-existing music. The book moves beyond the simplistic generalizations of much previous scholarship tackling the themes, to outline complex realities pertaining to a series of examples. It focuses on the connection between quotation and quoted text, and specifically the idea that the former inherently refers outwards, from its position within a film, to the latter as it exists in the world beyond the screen. The book shows that 'post-existing music': the music we now listen to and understand in new ways following its cinematic appropriation.