The hydroformylation reaction is an increasingly important chemical synthesis route, as it is one of the few reactions through which a single carbon atom can be added onto a long chain species. The combination of a high volume of hydroformylation products produced commercially, the growing importance of chiral synthesis in pharmaceutical applications, and an increasing awareness of energy use and environmental constraints has led to extensive evaluations of hydroformylation reactions in benign reaction solvents, and in particular, supercritical carbon dioxide (scCO(2)). Since the catalysts used are most often homogeneous in nature, dissolved into the solvent or reactan/product mixture, the use Of scCO(2) not only improves the environmental profile of hydroformylation processes but also improves the ability to recover the often expensive rhodium-based catalysts. The current review describes recent developments in the design of catalysts for hydroformylation in scCO(2), in the use of these catalysts for hydroformylation of alpha-olefins to form linear aldehydes and for asymmetric hydroformylation of styrene, and the effect of the supercritical fluid solvent on these reactions. (c) 2006 Elsevier B.V. All rights reserved.