The Nuclear Notebook is researched and written by Hans M. Kristensen, director of the Nuclear Information Project with the Federation of American Scientists, and Matt Korda, a research associate with the project. The Nuclear Notebook column has been published in the since 1987. This issue’s column examines tactical nuclear weapons in world nuclear arsenals. Since the end of the Cold War, inventories have declined by an order of magnitude from 20,000–30,000 to about 2,500 today. Both the United States, Pakistan, and Russia are modernizing their tactical nuclear arsenals, adding new types to the inventory and increasing the role and salience of tactical nuclear weapons in their military strategies. Moreover, tactical nuclear weapons are being used to undermine existing arms control agreements. These trends threaten to re-create some of the dynamics that during the Cold War triggered an arms race and dangerous escalation strategies that increased the risk of nuclear war.