The peroxisome is a ubiquitous, subcellular organelle containing more than 50 matrix enzymes that participate in a diverse array of metabolic pathways. Failure to assemble normal peroxisomes is the cellular hallmark of Zellweger syndrome and other human disorders of peroxisome biogenesis. Identification of the genes required for peroxisome biogenesis is proceeding at a rapid pace helped immeasurably by work in other species, particularly various yeasts. The ultimate goals of this effort are to identify all of these genes and to understand how their protein products interact to produce normal appearing and functioning peroxisomes. Attainment of these goals will lead to a better understanding of the peroxisome biogenesis disorders, their pathophysiology and treatment.