The peroxisome biogenesis disorders (PBD) are a heterogeneous group of autosomal recessive disorders in which peroxisome assembly is impaired, leading to deficiencies of peroxisomal enzymes, complex developmental sequelae and progressive disabilities. Mammalian peroxisome assembly involves the coordinated action of multiple PEX proteins, or peroxins, encoded by PEX genes. There are two main groups of PBD: Zellweger spectrum disorder, due to defects in any one of 13 PEX genes, and Rhizomelic Chondrodysplasia Punctata spectrum, mainly due to defects in PEX7. For most patients, there is a correlation between clinical severity and effect of the mutation on PEX protein function. Diagnosis relies on biochemical measurements of peroxisome metabolites and enzymatic functions, PEX gene sequencing and, in some cases, analysis of peroxisome morphology and more detailed studies of peroxisome biology. Recent advancements in diagnosis have expanded the phenotypes observed, indicating that the full spectrum of these disorders remains to be identified. Although there are no targeted therapies, improved knowledge of peroxin functions, continued characterization of disease models, and systematic clinical studies are expected to impact treatment in the near future.