This book is an overview of the U.S. nuclear stockpile and the issues relating to maintenance and replacement of warheads. Nuclear weapons will continue to play a key role in U.S. security policy for many decades. At issue for Congress is how best to maintain the nuclear stockpile so that it will retain, for many decades, capabilities that political and military leaders deem necessary. Three main options are discussed in this book: (1) extending the service lives of current warheads without nuclear testing; (2) developing, building, and deploying a new generation of warheads without testing to replace the current stockpile; or (3) resuming nuclear testing, which the United States suspended in 1992, as a tool to help maintain existing warheads or develop new ones. This book focuses on the first two options and compares how they respond to congressional goals, presenting pros, cons, uncertainties, costs and potential risks and benefits, then discusses issues for Congress. This is an edited, excerpted and augmented edition of a CRS Report, U.S. Department of Energy and GAO publications.