The Strategic Defense Initiative (SDI) was a proposal by U.S. President Ronald Reagan on March 23, 1983 Federation of American Scientists. blank">Missile Defense Milestones. Accessed March 10, 2006. to use ground-based and space-based systems to protect the _United States from attack by strategic nuclear ballistic missiles. The initiative focused on strategic defense rather than the prior strategic offense doctrine of mutual assured destruction (MAD).

Though it was never fully developed or deployed, the research and technologies of SDI paved the way for some anti-ballistic missile systems of today. The Strategic Defense Initiative Organization (SDIO) was set up in 1984 within the United States Department of Defense to oversee the Strategic Defense Initiative. It gained the popular name Star Wars after the 1977 movie by George Lucas. Under the administration of President Bill Clinton in 1993, its name was changed to the Ballistic Missile Defense Organization (BMDO) and its emphasis was shifted from national missile defense to theater missile defense; from global to regional coverage. BMDO was renamed to the Missile Defense Agency in 2002. This article covers defense efforts under the SDIO.