Elucidation of gene regulatory networks (GRNs) underlying aspects of leaf development in multiple model species has uncovered surprisingly plastic regulatory architecture. The meticulously mapped network interactions in one model species cannot now be assumed to map directly onto a different species. Despite these overall differences, however, many modules do appear to be almost universal. Extrapolating findings across different model systems will demand great care but promises to reveal a rich tapestry of themes in GRN architecture and regulation. The purpose of this review is to approach the field of leaf development from the perspectives of the evolution of developmental systems that orchestrate leaf development.