The international politics of combating piracy and other threats to maritime security in Southeast Asia are difficult, to say the least. On the one hand, there is a common interest among both regional states and their extraregional partners for an for improved sea line of communication (SLOC) and energy security. On the other, diverging strategic interests and varying political cultures and sensitivities vastly complicate any effort to eliminate the threat in a practical way. The desire to protect national sovereignty usually trumps efforts to effectively combat the threat, a particular shortcoming when dealing with a problem which is inherently transnational in nature and requires multinational cooperation to be overcome. Moreover, the habit of some states of focusing maritime-security cooperation efforts on multilateral institutions rather than on more active cooperation on the water may simply be a politically expedient way to avoid making difficult choices. This chapter identifies and assesses the effectiveness of four leading drivers of maritime security cooperation to combat piracy and related threats in Southeast Asia: the multilateral institutional framework; Japanese-led initiatives; U.S.-led initiatives; and other, nonmultilateral cooperation.