The Bureau of International Security and Nonproliferation (ISN) is a bureau within the United States Department of State responsible for managing a broad range of nonproliferation and counterproliferation functions.

Stephen G. Rademaker was the first Acting Assistant Secretary of State for International Security and Nonproliferation.

The Bureau's role within the Department of State is to spearhead efforts to promote international consensus on WMD proliferation through bilateral and multilateral diplomacy.

The ISN Bureau is also tasked to address WMD proliferation threats posed by non-state actors and terrorist groups by improving physical security, using interdiction and sanctions, and actively participating in the Proliferation Security Initiative.

It seeks to work with international organizations such as the United Nations, the G7, NATO, and the International Atomic Energy Agency to reduce and eliminate threats posed by weapons of mass destruction, and to support foreign partners in their efforts.