Right after I graduated, I interned with the Arms Control Association. It was terrific.

– George Stephanopolous
Host of ABC's This Week
January 1, 2005
Threshold Test Ban Treaty (TTBT)

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The Threshold Test Ban Treaty (TTBT) between the United States and the Soviet Union establishes a nuclear threshold through the prohibition of nuclear tests that exceed 150 kilotons. The threshold prevents the testing of new or existing nuclear weapons that exceed the fractional-megaton range. The United States and Soviet Union are subject to verification provisions. These are conducted through hydrodynamic yield measurements, seismic monitoring, and on-site inspections.

Opened for Signature: 3 July 1974

Entry into force: 11 December 1990

Official Text: http://www.state.gov/t/isn/5204.htm#treaty

Status and Signatories: http://www.state.gov/t/isn/5204.htm#narrative

ACA Backgrounder: https://www.armscontrol.org/factsheets/Nuclear-Testing-and-Comprehensive-Test-Ban-Treaty-CTBT-Timeline