Auxin has been implicated in a vast array of plant processes, and concomitant with a more detailed understanding of the cellular mechanisms underlying its biosynthesis, transport, and perception, it has become increasingly clear that auxin also has instructive roles in plant pattern formation. Moreover, it turns out that in a multitude of instances, from the early establishment of body axes to organogenesis in shoot and root, plant tissue patterns owe their robust flexibility in part to feedback interactions involving auxin. Higher resolution cell biology, molecular genetics, and genomics, as well as live imaging are now used together to define the parameters needed to generate more detailed and precise mathematical models of plant development.