This book provides the first comprehensive and empirically informed analysis of the protective principle of extraterritorial criminal jurisdiction. This book provides, for the first time in recent history, a reconsidered, innovatively conceptualised exposition of the principle. It goes further to provide new insight on how States have used protective principle jurisdiction. It also identifies and defines vital interests and provides a typology of interests included under the ambit of the protective principle lex lata. This is an important work bringing much needed clarity to (at times) a controversial legal principle.