"A new nuclear arms race is underway between Russia and the United States, one that focuses on the technology of delivery of nuclear warheads. This book describes how and why this race is happening, who still possesses nuclear weapons, and what constraints apply to those weapons under international law. A global nuclear ban treaty entered into force in January 2021, but the nuclear powers kept distant. The last remaining treaty restraining the arsenals of the two nuclear superpowers will expire in less than five years' time and the risk is that other States will turn to nuclear arms for their defence, further fracturing the non-proliferation regime installed after the Cuban missile crisis"--