This chapter discusses the complex law of copyright joint authorship and joint ownership with regard to musical works. It shows that joint authorship under UK law depends upon collaboration of musical co-authors, and on original contributions from them towards the finished work. The contributions must be merged, so that they are not distinct. The contributions must also be of the correct kind, that is to say, contributions towards the expressive form that is protected by copyright. Keywords: copyright authorship; musical works; copyright co-ownership; joint ownership; German authors’ rights law; US copyright law.