Most philosophical accounts of emergence are based on supervenience, with supervenience being an ontologically synchronic relation of determination. This conception of emergence as a relation of supervenience, I will argue, is unable to make sense of the kinds of emergence that are widespread in self-organizing and nonlinear dynamical systems, including distributed cognitive systems. In these dynamical systems, an emergent property is ontological (i.e., the causal capacities of P, where P is an emergent feature, are not reducible to causal capacities of the parts, and may exert a top-down causal influence on the parts of the system) and diachronic (i.e., the relata of emergence are temporally extended, and P emerges as a result of some dynamical lower-level processes that unfold in real time).