In the twenty-first century, the U.S. military has increasingly been called upon to conduct civil development activities as part of reconstruction and stabilization operations or recovery from natural or man-made disasters. These activities overlap development activities of both the U.S. Department of State (DoS) and U.S. Agency for International Development (USAID). Three D (Defense, Diplomacy and Development) coordination is a subset of interagency coordination that provides a forum for DoD, DoS, and USAID to collaborate and align efforts in order to create synergy and avoid wasting resources in pursuit of national interests. This paper provides the current status of Three D efforts in Washington, DC and at the Combatant Command level, speaks to Three D coordination challenges, and details some of the best practices being used either as Three D or interagency coordination efforts. It also links the requirement to coordinate to National level documents including the National Security Strategy and subordinate strategies, the Quadrennial Defense Review, Joint publications, USAID s Civilian-Military Operations Guide, and the pre-decisional draft 3D Planning Guide, Diplomacy, Development, Defense, a Three D product of the Joint Staff, DoS and USAID.