This chapter examines the related but distinct concepts of practice, custom, and usage; and how and the extent to which they ‘form part of the fabric’ of shipping law. It suggests that although it might be more accurate to speak of commercial custom, usages, and practices as an influence on the development of commercial law rather than as a source, they are very clearly part of the fabric of commercial jurisprudence. Their contribution may have diminished as the practice of domestic and international commerce has become more closely managed, professionalized, bureaucratic, and harmonized, with a proliferation of standard form documentation, and the promulgation of unified rules of practice. But their potential influence and contribution remains. These concepts are of equal application to litigation and arbitration, and the same legal framework and preconditions to validity apply, as also do the rules relating to burden and standard of proof.