This major study advances an interpretation of criminal justification defences that views them as an integral component of the structure of the criminal law. Criminal law is defined here as the institutional representation of the underlying principles of political morality in a liberal society. The book extends the traditional scope of the legal and philosophical discussion of justification defences. It integrates philosophical analysis with a consideration of contemporary applications, it shows how these defences are key components of criminal law, and it explores the relationship between legal and moral justification.