Since the events of September 11, 2001, improving the security of our nations drinking water and wastewater infrastructure has become a top priority. The U.S. Environmental Protection Agency (EPA) plays a critical role in this effort as the federal agency lead for water security. In March 2004, EPA released the peer-reviewed Water Security Research and Technical Support Action Plan (Action Plan), which identified important issues for the drinking water and wastewater industries, outlined research and technical support needs to address those issues, and presented a list of projects to be undertaken in response to the identified needs. This document describes the progress in addressing the issues identified in the Action Plan. The National Homeland Security Research Center (NHSRC) in the Office of Research and Development (ORD) and the Water Security Division (WSD) in the Office of Water (OW) led the development of the Action Plan, which mobilized a wide range of partners. During the development of the Action Plan, these partners helped identify critical technical support and research projects needed to ensure the security of the nations drinking water and wastewater systems. These needs form the core of the Action Plan. The various partnerships initiated by EPA will continue to be of critical importance as the Action Plan is implemented and updated. The completion of the Action Plan marked a major step towards developing a comprehensive research strategy to protect the countrys water infrastructure. Much has been accomplished since the release of the Action Plan. Partners have joined together to address the multiple concerns facing the nations water sector.