What is Buddhist monastic law? How should one think about its key texts, institutions and principles? This chapter answers these questions in the context of Sri Lanka and other parts of South and Southeast Asia, focusing especially on ideas of unity and diversity in law. The first part of this chapter summarises key ideas and principles found in the ancient code of monastic law, the Vinaya Piṭaka, which is thought to be the cornerstone of monastic legal texts and practices. The second (longer) part of this chapter introduces readers to a range of monastic legal sources outside the Vinaya Piṭaka, which also play key roles in the practice of monastic law in contemporary Sri Lanka. These sources include commentaries, constitutions, handbooks, judicial manuals, statutes, case law, social expectations and other normative sources produced by monks, state officials and Buddhist laypersons.