Three-membered heterocyclic rings offer a powerful combination of reactivity, stability, availability, and atom economy. While heteroatom-based nucleophiles have been successfully employed, the use of carbon-centered nucleophiles is much less developed, yet represents a significant advance since it builds the basic carbon framework. In fact, the asymmetric ring-opening of epoxides and aziridines with carbonbased nucleophiles, as will be discussed in this Microreview, offers the possibility of generating valuable, chiral, nonracemic building blocks in a very simple, stereodefined manner. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).