Helen Mary Caldicott (born 7 August 1938) is an Australian physician, author, and anti-nuclear advocate who has founded several associations dedicated to opposing the use of nuclear power, depleted uranium munitions, nuclear weapons, nuclear weapons proliferation, and military action in general.
In the late 1970s and early 1980s, Caldicott became a leader in the anti-nuclear movement in the United States through her role in reviving the organization Physicians for Social Responsibility and her role along with Randall Forsberg as one of the leaders of the Nuclear Freeze Movement.
She has continued to publicise her concerns, dividing her time between the United States and Australia and lecturing on nuclear energy, weapons and power, notably on the Fukushima nuclear meltdown.