Although Messiaen wrote extensively about his own music and compositional techniques, the central role of musical borrowing in his creative process has only recently been recognized. This chapter addresses the full range of sources and transformational techniques used by the composer to invent and assemble his musical materials, the evolution of his ‘borrowing technique’ across the course of his career, and the difficulties raised by the potential meanings that may be attributed to some of his borrowings. Attention is given to the contemporary musical practices from which Messiaen’s borrowing technique may have emerged, possible contextual reasons for Messiaen’s ambiguous attitude towardsexplaining his processes, and the rare critical responses to Messiaen’s music that suggest that a handful of listeners during his lifetime understood aspects of this creative technique.