Switzerland ratified the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in 1999. However, the entry into force of the CTBT depends on the ratification of all states involved. The international organisation responsible for implementing the treaty (Comprehensive Nuclear-Test-Ban Treaty Organisation, CTBTO) is working on a provisional basis as a so-called Preparatory Commission until the CTBT enters into force.

The Swiss Mission actively participates in the work of the Preparatory Commission and its working groups. Switzerland chaired the Commission in 2023. Switzerland is one of the twenty largest contributors to the regular budget of the Preparatory Commission and participates in the International Monitoring System of the CTBT with a seismic monitoring station in the Davos region.