The National Nuclear Security Administration's (NNSA) Tritium Readiness Program aims to establish an assured domestic source of tritium, a key isotope used in nuclear weapons, in order to maintain the U.S. nuclear weapons stockpile. Because tritium decays at a rate of 5.5 percent annually, it must be periodically replenished in the stockpile. However, since 2003, NNSA's efforts to produce tritium have been hampered by technical challenges. In this context, GAO was asked to (1) determine the extent to which NNSA has been able to overcome technical challenges producing tritium, (2) determine the extent to which NNSA is able to meet current and future nuclear weapons stockpile requirements for tritium, and (3) assess the management of NNSA's Tritium Readiness Program. To do this, GAO visited facilities involved in tritium production and reviewed tritium requirements established by NNSA and the Department of Defense, among other things. GAO recommends that NNSA develop a plan to manage tritium releases from reactors, analyze alternatives to its current tritium production strategy, ensure its contracting complies with appropriate contracting procedures, and ensure its future budget requests account for the program's large unexpended balances. NNSA generally agreed with our recommendations.