1959-60 Moratorium on testing implemented by the US, UK, and USSR.
1963 Partial Test Ban Treaty signed by the same three powers bans tests in the atmosphere, under water, and in outer space; the signatories agree to work towards a ban on underground tests.
1970 Non Proliferation Treaty commits the nuclear powers to continue negotiations towards a Comprehensive Test Ban (CTB) treaty.
1974 Threshold Test Ban Treaty agreed by US and USSR bans tests over 150 kilotonnes.
1976 Peaceful Nuclear Explosion Treaty sets further limits on the size of explosions.
1977-80 The US, UK and USSR resume direct discussions on testing.
1982 The US breaks off the discussions.
1982-83 The Conference on Disarmament (CD) in Geneva sees the establishment of a Verification and Compliance Working Group, but the group is not mandated to restart negotiations.
1984-89 The CD fails to obtain consensus on a mandate for talks.
1985-87 The USSR implements a unilateral moratorium.
1987 The US and USSR announce an agreement to revise the Threshold and Peaceful Nuclear Explosion treaties, and work towards a comprehensive test ban.
1990-92 The CD's ad hoc committee begins further discussions under a non-negotiating mandate.
1991 The USSR announces another unilateral moratorium of one year, subsequently extended by Boris Yeltsin.
1992 The US and France each declare a one-year unilateral moratorium. UK tests in the US are consequently halted, and the US moratorium is extended by Bill Clinton.
1993 The CD agrees a negotiating mandate for test-ban talks.
1994 CD's ad hoc committee begins negotiations.
1995 Non-Proliferation Treaty extended indefinitely. Signatories commit themselves to a CTB treaty "no later than 1996". However, France announces it would carry out more tests before signing that treaty.
September 1995 "True Zero" CTB, which would ban the smallest tests, endorsed in theory by France, the US, UK and Russia.
February 1996 France completes series of six tests.
July 1996 China announces that it has carried out its last test explosion.
Source: Verification Technology Information Centre