From Wikipedia,

The Treaty on the Prohibition of Nuclear Weapons (TPNW), or the Nuclear Weapon Ban Treaty, is the first legally binding international agreement to comprehensively prohibit nuclear weapons with the ultimate goal being their total elimination. It was adopted on 7 July 2017, opened for signature on 20 September 2017, and will enter into force on 22 January 2021.

For those nations that are party to it, the treaty prohibits the development, testing, production, stockpiling, stationing, transfer, use and threat of use of nuclear weapons, as well as assistance and encouragement to the prohibited activities. For nuclear armed states joining the treaty, it provides for a time-bound framework for negotiations leading to the verified and irreversible elimination of its nuclear weapons programme.

A mandate adopted by the United Nations General Assembly on 23 December 2016 scheduled two sessions for negotiations: 27 to 31 March and from 15 June to 7 July, 2017. The treaty passed on schedule on 7 July with 122 in favour, 1 against (Netherlands), and 1 official abstention (Singapore). 69 nations did not vote, among them all of the nuclear weapon states and all NATO members except the Netherlands.

While people are skeptical that this ban will cause any current nuclear state to imminently give up their nuclear weapons, it still may have the effect of preventing current non-nuclear states from gaining nuclear weapons. This mirrors the goal of the Treaty on the Non-Proliferation of Nuclear Weapons.