This chapter reviews the modern cases on the ‘third source’ in England and Wales and around the Commonwealth. This review illustrates that the law is fundamentally uncertain on the legal nature and exact provenance of these powers within each jurisdiction surveyed. It also illustrates that basic questions of legal theory relating to official empowerment and official action are unavoidable in the context of non-statutory executive powers. This demonstrates the gap between theory and practice in a specific context and justifies the need for the basic and wide-ranging interrogation of the law of judicial review undertaken in the book.