Fumonisins are mycotoxins produced by several widespread fungal pathogens of corn. Ingestion of fumonisin contaminated food and feeds causes several fatal diseases in livestock and is associated with esophageal cancer and neural tube defects in humans. In the recent years, fumonisin research has become one of the most active areas in fungal secondary metabolism. The gene cluster (FUM) required for fumonisin biosynthesis in Fusarium verticillioides has been cloned. The FUM genes are predicted to encode various fascinating enzymes, including a seven-domain iterative modular polyketide synthase (PKS), the first example of a fusion protein between the two subunits of serine palmitoyltransferase, a naturally fused cytochrome P450 monooxygenase and reductase, and a "stand-alone" nonribosomal peptide synthetase complex. This review highlights the progress in the studies of the molecular mechanism for fumonisin biosynthesis.