All multicellular organisms experience physiological changes with age, a phenomenon known as ageing. However, do they all senesce? Following Hamilton’s work, senescence, or the decrease in survival and/or fecundity with age, has become a dogma of life history theory. Indeed, the “wear-and-tear” of life is considered something of a law of life by the non-scientific population. Still, field research has highlighted some species that seem not to age (e.g., alligators, hydra, bristlecone pine). Furthermore, new theories have refuted the inexorable nature of senescence, using key organisms as examples. This symposium will (i) introduce new theoretical frameworks for the evolution of senescence, (ii) incorporate the latest ecological and evolutionary experimental research on senescence across the tree of life (plants, fungi and animals), (iii) explore the role of proxies to fitness other than age (e.g., development and size) on the evolution of senescence, and (iv) provide a more mechanistic understanding of senescence by bridging the gap between physiology and demography.