Care of humanity and of Earth and its ecosystems is the precondition for both justice and peace. Human beings, creatures, and plants are part of a web of life that depends on Earth for its sustenance. None are on Earth of their own choice. As the most intelligent of living beings, gifted with a moral sense, humans share responsibility to help humans, animals, and Earth itself — its air, water, plants, trees — to flourish. Science, as the instrument of reason, should be dedicated to creating peace and justice, and therefore nurturing life in human societies, among nations, and in nature. This approach stands in opposition to the war and militarism model, and to the market mentality that reduces life to the individual pursuit of material gain. The economy depends for its functioning on Earth’s ecosystems and social systems. Yet unrestrained greed, commodification, and consumerism are destroying ecosystems and rending societies by unjust, unsustainable inequality. Peace, justice, and ecological sustainability are indivisible and science must foster all three. Science for Peace is grounded in these understandings.