The U.S. National Archives and Records Administration's Electronic Records Archives (ERA), built to hold the avalanche of electronic records being created by the federal government of the United States, recently reached a major milestone. On September 30, 2011 ERA's initial development phase ended and the operations and maintenance phase began. Begun in 2005, ERA incrementally deployed important functions starting in 2008, when the National Archives and Records Administration (NARA) started ingesting its existing collection of electronic records into ERA and piloting the records management functions that allow federal agencies to create records schedules and transfer their permanent electronic records to NARA.As of January 30, 2012 ERA was storing more than 131 terabytes of records in a wide variety of formats from the United States Congress, federal Agencies, and the George W. Bush White House. This volume is just the beginning of what ERA will manage and store, though. For example, NARA has recently received around 300 terabytes of electronic records from the 2010 Census, currently being prepared for ingest into ERA. NARA is relying on ERA every day to perform a key part of its basic mission, and ERA provides a flexible foundation on which NARA can build increasingly sophisticated functions over time.ERA's successes are critical to the mission of the archives, but the challenges the project encountered and the lessons NARA learned along the way may be more valuable to the digital preservation community. This paper will provide a summary of what ERA is and highlights of the project's accomplishments, but will also discuss important decision points in planning and development, external constraints, lessons learned from the experience, and challenges remaining in the future. Lessons learned include the importance of project governance, strategies for maintaining control of the project, and the necessity of constantly communicating to ensure that stakeholder expectations are realistic. Challenges included managing a large number of disparate requirements for records governed under different legal frameworks and working under the constraints of legally mandated timeframes for records ingest and access. NARA's response to these challenges involved a solution architecture that includes a common architectural pattern shared by different instances within a system of systems. NARA will be relying on this flexible software framework, along with standardized interfaces and data elements, to adapt ERA now that the system has moved out of initial development and into the operations and maintenance phase.