Australia and the United States have found themselves fighting common enemies on the battlefields of the world for over half a century. Australian ground forces have repeatedly stood shoulder-to-shoulder with American troops in conflicts from Korea and Vietnam to Afghanistan – and now in the 2003 Iraq war. This study looks closely at the key factors which, for over fifty years, have shaped, interpreted and applied the aims and aspirations of this mutual defence agreement to the real world of shifting threats, changing strategic balances and the democratic uncertainties of domestic politics. A departure from the current literature, the ANZUS alliance, now updated to take account of the new post 11 September 2001 realities, is presented as an accessible and concise survey of this often neglected but increasingly important trans-Pacific link between the American giant and its durable Australian ally. Suitable as supplementary reading at the 3rd year undergraduate and postgraduate levels of courses studying international relations generally, but also useful for those engaged with elements of global and regional security, and strategic defence analysis.