Among other things, the 199798 East Asian financial crisis has led to questioning within the Association of Southeast Asian Nations (ASEAN) about whether the region needs a common currency. This paper aims to discuss the underlying economic issues and prospects, from both a theoretical and a practical point view. The analysis focuses only on the five largest ASEAN nations. Standard criteria suggested by the theory of Optimal Currency Areas are reviewed and applied to the region. The paper then provides a discussion on possible steps that can be pursued to realise currency union.