The United States and Russia have started negotiations on deep cuts in their nuclear arsenals, which together account for 95% of the world’s 27,000 warheads. Other key steps include bringing into force the Comprehensive Nuclear Test Ban Treaty; negotiating a verifiable treaty to end production of fissile material for use in weapons; radically improving the physical security of nuclear and radioactive materials, which is vital to prevent them from falling into the hands of terrorists; and strengthening the IAEA.