In this lecture I shall discuss the ancient divide between conceptions of the world as composed of things— ultimately unchanging atoms—and as process, in which the only constant is change. Focusing on organisms, and looking at metabolism, life cycles and symbiosis, I shall outline a range of reasons why the living world, in particular, must be seen as processual, as consisting of a hierarchy of processes at a range of spatial and temporal scales. I shall point out some of the more noteworthy consequences of this position for biology and philosophy, and briefly mention some reasons for thinking that the non-living world should also be understood as processual.