We are excited to bring together recent research on the molecular biology of Axenfeld-Rieger syndrome (ARS) disorders. In the following chapters we will review and provide direct evidence for the molecular basis of this group of heterogeneous disorders, which include Rieger syndrome and Rieger anomaly. While ARS patients were initially diagnosed in the early 1930s the genetic basis for ARS was unknown until the recent identification of chromo somal loci associated with this genetic disorder. In the mid-1990s Drs. Jeffrey C. Murray and Elena V. Semina identified PITX2 through positional...