This chapter investigates the identity and persistence conditions for processes as a task of biological process ontology. It argues that the problem of intrinsic variation in evolution, development, and metabolism motivates viewing biological individuals as processes rather than as substances. Different criteria of identity for processes are then evaluated, including causal and spatio-temporal relations. The chapter ultimately settles on the view that processes are individuated by causal cohesion and are identical if they share the same cohesive properties and spatio-temporal region. The persistence of processes is interpreted on the model of perdurance, as a form of causal continuity or genidentity.