Several major advances in our understanding of the structure, function and properties of biological iron-sulfur clusters have occurred in the past year. These include a new structural type of cluster in the inappropriately named prismane protein, the establishment of redox-mediated [Fe2S2]2+ <--> [Fe4S4]2+ cluster conversions, and the characterization of valence-delocalized [Fe2S2]+ and all ferrous clusters with [Fe2S2]0, [Fe3S4]2- and [Fe4S4]0 cores. The emergence of novel types of redox, regulatory and enzymatic roles have also raised the possibility of iron-sulfur clusters mediating two electron redox processes, coupling proton and electron transfer, and catalyzing disulfide reduction and reductive cleavage of S-adenosylmethionine via sulfur-based cluster chemistry.