In the transitional economies of Cambodia, the Lao People's Democratic Republic, and Viet Nam (the CLV countries), foreign currencies such as the US dollar commonly circulate in addtion to the local currency. National authorities must consider the costs and benefits of such a system, especially in relation to monetary and exchange policies' effect on their development priorities. "This pioneering study is an important contribution to understanding the underpinnings of the Mekong economies' dynamism...Highly recommended." -- Hal Hill, H.W. Arndt Professor of Southeast Asian Economies, Austratlian National University While dealing with multiple currencies is ultimately an issue of national economic policy, the CLV countries could benefit from greater regional cooperation on monetary and financial issues. They would be able to exploit economies of scale, introduce best practices, and facilitate the adoption of common regulatory standards. Greater regional dialogue on monetary policy could also help the CLV countries find a solution to the so-called multiple-currency phenomenon and reap more benefits from their increasing regional economic interdependence. This study, conducted by a team of economists from the Asian Development Bank, academics, and personnel from CLV finance ministries and central banks, explores the issues of multiple currencies and regional monetary cooperation among the economies of the Association of Southeast Asian Nations (ASEAN) in the context of increasing regional economic interdependence. It reviews the main issues related to the monetary and exchange rate policy decisions taken by CLV national authorities, and discusses the options and opportunities available for enhancing monetary and financial stability in the ASEAN region.