Most current U.S. nuclear warheads were built in the 1970s and 1980s and are being retained longer than was planned. Yet they deteriorate and must be maintained. To correct problems, a Life Extension Program (LEP), part of a larger Stockpile Stewardship Program (SSP), replaces components. Modifying some components would require a nuclear test, but the United States has observed a test moratorium since 1992. Congress and the Administration prefer to avoid a return to testing, so LEP rebuilds these components as closely as possible to original specifications. With this approach, the Secretaries of Defense and Energy have certified stockpile safety and reliability for the past 12 years without nuclear testing. NNSA argues it will become harder to certify current warheads with LEP because small changes may undermine confidence in warheads, perhaps leading to nuclear testing, whereas new-design replacement warheads created by the RRW program will be easier to certify without testing. Critics believe LEP and SSP can maintain the stockpile indefinitely. They worry that untested RRWs may make testing more likely and question cost savings, given high investment cost. They note that there are no military requirements for new weapons. Others feel that neither LEP nor RRW can provide high confidence over the long term, and would resume testing. Another point of view is that either LEP or RRW will work without nuclear testing. This report provides background and tracks legislation. It will be updated to reflect final FY2010 congressional action on RRW. See also CRS Report RL33748, Nuclear Warheads: The Reliable Replacement Warhead Program and the Life Extension Program, by Jonathan Medalia, which compares these two programs in detail.