At the beginning of 2005, Southeast Asian security cooperation is still regarded as inadequate to defend the region against maritime threats. However, structural, economic and normative factors are enabling greater cooperation in the post-9/11 "Age of Terror". This article opens with a brief outline of the history of Southeast Asian maritime security cooperation from 1990 to December 2004, and then discusses the various maritime threats faced by the region. It next describes five factors that are enabling greater maritime security cooperation in the Age of Terror. The potential application of those factors is assessed to anticipate the most likely forms of future regional cooperation. While cooperation will expand on many levels the most fruitful cooperation will result from improved networks of bilateral relationships. Information in this working paper will be of interest to those seeking to understand the cooperation and security dynamics of this important and intensely maritime region. It should be of specific interest to those policymakers seeking to improve international cooperation to combat Southeast Asian transnational maritime threats such as terrorism, piracy and smuggling.