Morphogenesis of leaf shape and formation of the major elements of leaf vasculature are temporally coordinated during leaf development. Current analyses of mutant phenotypes provide strong support for the role of auxin signaling in vascular pattern formation and indicate that leaf shape and vasculature are developmentally coupled. Two other mechanisms that may contribute to the regulation of these processes are a diffusion-reaction system and long-distance signaling of informational macromolecules.