Abstract: Leaf is the first lateral organ produced by the activity of the shoot apical meristem (SAM). Early leaf development is artificially divided into three main stages: the initiation of leaf primordium, the establishment of leaf adaxial-abaxial polarity, and the expansion of leaf blade. Numerous of evidence indicates that leaf development is regulated by inner genetic mechanism and outer environmental cues. Phytohormones, especially auxin, play essential roles in coordination of these two regulation mechanisms. Auxin homeostasis, polar transport and signaling affect the whole progress of leaf development. In this mini-review, we will summarize recent progress of auxin regulation in leaf development and morphogenesis, and try to understand the complex regulation network of leaf development.