The Comprehensive Nuclear-Test-Ban Treaty (CTBT) prohibits all nuclear weapon test explosions or other nuclear explosions. In order to verify compliance with its provisions, the Treaty establishes a global network of monitoring facilities and allows for on-site inspections of suspicious events. The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) was set up in 1996 with its headquarters in Vienna, Austria. It is an interim organization tasked with building up the CTBT verification regime in preparation for the Treaty's entry into force, as well as encouraging all countries to sign and ratify the Treaty.
One hundred and eighty-three countries have signed the Treaty, of which 164 have also ratified it, including three of the nuclear-weapon states: France, the Russian Federation and the United Kingdom. But forty-four specified countries that possess nuclear technology must sign and ratify before the CTBT can enter into force. Of these, eight are still missing: China, Egypt, India, Iran, Israel, North Korea, Pakistan and the USA. India, North Korea and Pakistan have yet to sign the CTBT.