The WT1 gene was originally identified through its involvement in the development of Wilms tumours. The gene is characterized by a plethora of different isoforms with, in some cases, clearly different functions in transcriptional control and RNA metabolism. Many different mouse models for Wt1 have already been generated, and these are increasingly providing new information on the molecular roles of Wt1 in normal development and disease. In this review we discuss the different models that have been generated and what they have taught us about the role of Wt1 in the kidney.