In the late 1940s, the Soviet Union rushed to build and test its first nuclear bomb to reach parity with the United States. The Soviet government chose the steppes of Kazakhstan as its first nuclear-testing site. In difficult conditions, weapons program participants built the site and, in 1949, tested the first Soviet nuclear bomb. Shrouded in secrecy, the Soviet military complex continued to conduct nuclear tests in Kazakhstan for forty years while the local population became an unwilling victim of the Soviet nuclear might. Nuclear tests, especially during the earlier years of atmospheric testing, resulted in severe health and environmental consequences for thousands of nearby residents. Mass protests in Kazakhstan against nuclear tests built the momentum that drove the Kazakh government's decision to close down the Semipalatinsk nuclear-testing site in 1989. Organized public movement against nuclear testing became an important part of Kazakhstan’s nation-building process. Since closing down the site, Kazakhstan has prioritized nuclear disarmament and nonproliferation, using its tragic nuclear past as a platform for making meaningful contributions to international security. Kazakhstan now offers the former nuclear-test site at Semipalatinsk for exercises designed to strengthen the verification capacity of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The country also plays a leading role in promoting CTBT entry into force.