The leaf is the major site of photosynthesis and the prototypical organ of terrestrial plants. The past five years have seen a dramatic increase in our understanding of the genetic control of leaf development. The establishment of determinacy, the role of the meristem, the establishment of polarity, the control of cell division, vascularization and epidermal patterning have all been the subject of genetic screens and many mutants have been isolated and characterized. Many of these mutants affect floral and embryonic structures, demonstrating the inherent similarities in all lateral organs. In this review we focus on the interactions between these genes and the networks that establish pattern in lateral organs.