On Friday, the United Nations’ Treaty on the Prohibition of Nuclear Weapons will enter into force. The agreement, ratified last October, is the world’s most ambitious treaty on nuclear weapons yet — 86 nations have signed it and 51 state parties have ratified it. But nuclear weapons states, as well as Japan, have refused to sign the treaty, preferring nuclear arms control treaties that they hope will eventually lead to the elimination of all weapons.

What are the treaty’s main obligations?

State parties that join the treaty must agree not to develop, test, produce, acquire, transfer, possess, stockpile or threaten to use nuclear weapons. The treaty also specifically prohibits the deployment of nuclear weapons on national territory and forbids providing assistance to any other state that tries to carry out any of the above activities.