 Process philosophy opposes ‘substance metaphysics,’ the dominant research paradigm in the history of Western philosophy since Aristotle. Substance metaphysics proceeds from the intuition—first formulated by the pre-Socratic Greek philosopher Parmenides—that being should be thought of as simple, hence as internally undifferentiated and unchangeable. Substance metaphysicians recast this intuition as the claim that the primary units of reality (called “substances”) must be static—they must be what they are at any instant in time. In contrast to the substance-metaphysical snapshot view of reality, with its typical focus on eternalist being and on what there is, process philosophers analyze becoming and what is occurring as well as ways of occurring. In some process accounts, becoming is the mode of being common to the many kinds of occurrences or dynamic beings. Other process accounts hold that being is ongoing self-differentiation; on these accounts becoming is both the mode of being of different kinds of dynamic beings and the process that generates different kinds of dynamic beings. In order to develop a taxonomy of dynamic beings (types and modes of occurrences), processists replace the descriptive concepts of substance metaphysics with a set of new basic categories. Central among these is the notion of a basic entity that is individuated in terms of what it ‘does.’ This type of functionally individuated entity is often labeled ‘process’ in a technical sense of this term that does not coincide with our common-sense notion of a process. Some of the ‘processes’ postulated by process philosophers are—in agreement with our common-sense understanding of processes—temporal developments that can be analyzed as temporally structured sequences of stages of an occurrence, with each such stage being numerically and qualitatively different from any other. But some of the ‘processes’ that process philosophers operate with are not temporal developments in this sense—they are, for example, temporal but non-developmental occurrences like activities, or non-spatiotemporal happenings that realize themselves in a developmental fashion and thereby constitute the directionality of time. What holds for all dynamic entities labelled ‘processes,’ however, is that they occur—they are in some fashion intimately connected to time, and often, though not necessarily, are related to the directionality or to the passage of time.