Fifty years ago, a small one and a half page paper withouta single reference was published in the leading journal Na-ture. The paper laid out the most general mathematical for-mulation of natural selection that would work for all kindsof selection processes and under any form of inheritance (notjust biological evolution and Mendelian genes), although thepaper discussed the issue in a genetical framework. Writ-ten by a maverick American expatriate in England, with noprior background of studying evolution or genetics, the paperhad initially been turned down by the editor of Nature as toodifficult to understand. Largely ignored by the evolutionarybiology community till the 1990s, the Price Equation is nowwidely recognized as an extremely useful conceptualization,permitting the incorporation of non-genetic inheritance intoevolutionary models, serving to clarify the relationship be-tween kin-selection and group-selection, unifying varied ap-proaches used in the past to model evolutionary change, andforming the foundation of multi-level selection theory.