William R. Moomaw spent the first third of his life learning. He received his PhD in physical chemistry from MIT. In the second third of his life he taught physical and environmental chemistry, and conducted molecular spectroscopy and photochemistry research at Williams College. In the third third of his life, he shifted to science diplomacy as the initial director of the Climate and Energy program at the World Resources Institute in Washington and then as the only chemist at the Fletcher School of Law and Diplomacy at Tufts University. There he founded a policy research center, and taught future scientist diplomats who now populate and direct many international organizations. He is now in the fourth third of his life having gained emeritus status in 2014. He continues to conduct climate mitigation and adaptation research, does some teaching, and engages the scientific community to develop sustainable solutions to global change problems.