This is the second in a series of four papers that discuss and present a model of human occupation. The first paper presented the structure and content of the model. This paper conceptualizes change according to the model. It introduces the systems concept of hierarchy into the model as a foundation for explaining its ontogenesis. Two facets of change are proposed. The first facet is a series of stages through which occupation is processed. The second is a description of ontogenesis through the life span from the perspective of temporal adaptation.