The fully updated and revised third edition of this widely used text provides a comprehensive survey of leading perspectives in the field including an entirely new chapter on Realism by Jack Donnelly. The introduction explains the nature of theory and the reasons for studying international relations in a theoretically informed way. The nine chapters which follow - written by leading scholars in Australia, Canada, New Zealand, the US and the UK - provide thorough examinations of each of the major approaches currently prevailing in the discipline.