Today, January 22, 2021, is a historic day. The Treaty on the Prohibition of Nuclear Weapons enters into force, three months after the 50th country, Honduras, ratified it. Nuclear weapons are now illegal under international law in every aspect. Possession is illegal; manufacture is illegal; use is illegal; threatening to use is illegal; transfer is illegal; aiding and abetting any of these things is illegal. I salute the International Physicians for the Prevention of Nuclear War, where the idea for this treaty originated — though its antecedents go much farther back — to the 1990s, when many non-government organizations, including IPPNW, created a mock treaty to ban nuclear weapons. The International Campaign to Abolish Nuclear Weapons (ICAN) was formed to bring the idea to fruition; it won the Nobel Peace Prize for doing so. It is a comprehensive treaty; no nuclear weapon states have signed it. There are nine: the United States, Russia (the successor nuclear state of the Soviet Union), Britain, France, China, Israel, India, Pakistan, and North Korea (though Israel does not confirm or deny possessing these weapons). The first five are parties to the 1970 Nuclear Non-Proliferation Treaty, whose Article VI requires them to negotiate “in good faith” to achieve nuclear disarmament. In the 1990s, the World Court interpreted this to mean actually achieving nuclear disarmament in all its aspects. Both the good faith and the achievement have been sorely lacking. Avoiding further humanitarian catastrophes that the manufacture, testing, and use of nuclear weapons have already created are at the heart of the treaty; so, of course, is preventing the true apocalypse of a nuclear war. Countless families since the first chain reaction was achieved at the University of Chicago on December 2, 1942 have suffered. IPPNW and IEER documented those disasters, so far as public information would allow, in three volumes published in the 1990s: Radioactive Heaven and Earth on testing;...