This chapter examines the use of borrowed material; that is, basing polyphony on existing music, whether plainchant or polyphony previously composed. The techniques described have intentionality in common: cantus firmus treatment of varying degrees of strictness, including paraphrase, ‘imitation’ technique (formerly known as ‘parody’), and more allusive forms. Special consideration is given to the different motivations for the practice (dating back to the origins of polyphony itself), ranging from symbolic or allegorical representation to emulation and competition between composers. Picking up from Chapter 8, the family of ‘L’Homme armé’ Masses offers a case-study of these relationships, but the practice of musical borrowing transcends any single genre, type, or destination. Equally remarkable is the possible range, scale, and scope of allusion, from overt quotation over an entire work to passing reference or evocation of a given technical parameter in ways that may not be directly audible. Finally, different types of borrowing reconfigure the relationship between composer, performer, and audience; these changing dynamics are closely considered.