Congenital disorders of glycosylation (CDGs) are a rapidly growing group of inherited disorders caused by defects in the synthesis and processing of the asparagine(ASN)-linked oligosaccharides of glycoproteins. The first CDG patients were described in 1980. Fifteen years later, a phosphomannomutase deficiency was found as the basis of the most frequent type, CDG-Ia. In recent years several novel types have been identified. The N-glycosylation pathway is highly conserved from yeast to human, and the rapid progress in this field can largely be attributed to the systematic application of the knowledge of yeast mutants. Up to now, eight diseases have been characterized, resulting from enzyme or transport defects in the cytosol, endoplasmic reticulum, or Golgi compartment. CDGs affect all organs and particularly the CNS, except for CDG-Ib, which is mainly a hepatic-intestinal disease.