 The terms of debate can in principle apply to the inorganic world; e.g., solar systems can “evolve” and could develop epigenetically. Yet they are not thought of as doing so, typically, and so epigenesis and preformation are primarily applied to the organic world. Species can evolve or develop more or less gradually, with more or less form already physically existing or programmed in from the beginning. Yet typically discussions of epigenesis and preformation have focused on individual organisms and their development rather than on species. The emphasis is on different interpretations of the actual developmental process as it plays out in time, in individual organisms. Therefore, this entry focuses on individual organisms and understandings of their development processes. Even more specifically, this means looking at the development of their form and to a lesser extent also function. Epigenesis and preformation offer two competing interpretations of what is involved, with a range of alternatives in between. The two approaches draw on different metaphysical and different epistemological sets of assumptions. We can get at the central issues by looking most closely at a series of focused episodes.