The American Recovery and Reinvestment Act (ARRA) of 2009 (Recovery Act) provided funding for 16 energy storage demonstration projects. The projects ranged in scope from feasibility studies and technology demonstrations to full-scale, operational energy storage plants. This investment had a signicant positive impact on the grid-connected energy storage industry. The goal of this report is to summarize the lessons learned from the ARRA projects, and to make recommendations for future Department of Energy (DOE) investments. Information for this report primarily came from three sources: a questionnaire and interview with each project team; DOE energy storage program peer review presentations; and DOE reports required as part of the ARRA project. Some lessons learned were common to many projects. Development of standards, codes and protocols specic to energy storage systems will mitigate uncertainty over code compliance, streamline permitting, and should be a priority (especially related to safety). Removal of regulatory barriers that preclude optimal operation of an energy storage system with multiple applications would immediately enable further deployment (e.g., FERC standards preclude the marketing department from reliability activities). Maturity of the approach to monetization varies substantially between applications with frequency regulation as an ancillary service leading other applications. Finally, developers focused on ramp mitigation and time shifting envision a reference plant. This reference plant would scale up from the current demonstration systems and would lead to the deployment of 50 MW-scale peaker plants.