Member states of ASEAN - the Association of South-East Asian Nations - have developed a distinctive approach to political and security co-operation. This approach builds on the principles of sovereign equality, non-intervention and non-interference, quiet diplomacy, mutual respect, and the principle of not involving ASEAN in mediating bilateral disputes among the membership. This is a new examination of the origins of ASEAN's diplomatic and security culture. It analyses how over time its key principles are practised and contested as member states respond to regional conflicts as well as challenges posed by the major regional powers, ASEAN's enlargement, and the Asian financial crisis. It also assesses whether ASEAN's diplomatic and security culture is likely to remain salient as the political, economic and security context in which regional leaderships operate undergoes further change.