The Leonard Medal Address

— The science of nucleosynthesis was substantially inspired by chemical analyses of meteorites. As if in repayment, that theory now imbues meteoritics with enlarged meaning. I recount the emergence of four great issues for nucleosynthesis—issues that received decades of my own attention; and I describe unexpected abundance patterns within meteorites that were suggested by the resolution of those issues. The latter have altered the information content of meteoritic science. The issues are: 1. a quantitative s ‐process theory 2. cosmoradiogenic chronology 3. explosive nucleosynthesis and gamma‐ray astronomy 4. cosmic chemical memory Starting from historical origins for each issue, I comment upon both the broad cultural canvas in which they lie and my own work in their establishment. Examples of predicted (or rationalized) meteoritic measurements illustrate our surprised delight at the expansion of the range and power of meteoritic science.