Emergence, the idea that in some sense more comes out of a system than was put in, is the holy grail of generative art. Yet emergence is a slippery concept. Originating in the philosophy of science, it has been taken up in systems theory, cognitive science and Artificial Life. As a consequence there are numerous definitions of emergence in the literature, but none well-suited to discussions of generative art. The paper reviews some existing definitions and proposes a new definition of generative-art emergence.