The chemistry and synthetic utility of lithiated aziridines are discussed. Lithiated aziridines can be easily generated and captured by electrophiles, leading to more highly functionalized derivatives. Nitrogen dynamics and complexation phenomena play crucial roles in determining the regiochemistry of the lithiation process of aziridines and the stereochemistry of the reactions of the resulting lithiated species with electrophiles. Bench experiments combined with spectroscopic investigations and density-functional theory calculations are particularly useful in elucidating the chemistry of aziridines in their carbanionic form and in unraveling new aspects of the chemistry of aziridines.The aziridine structural motif occurs frequently in natural products and in biologically active substances, and aziridines are common intermediates in organic synthesis. 1 Aziridines are readily accessible 2 in enantiomerically enriched forms and they are mainly used as electrophiles, taking advantage of their predictable, highly regioselective, ring-opening reactions with nucleophiles. Studies on lithiated epoxides and aziridines by my group and others have also demonstrated that there are many other less conventional, but nevertheless useful, reactions that these small-ring heterocycles can undergo. Indeed, when treated with strong bases such as lithium amides or organolithiums, aziridines can undergo α-deprotonation at the aziridine ring carbons to form lithiated derivatives that can be captured with an electrophile to give more substituted products. This lithiation-electrophile trapping sequence, which has been named the aziridinyl anion methodology and has been developed over the last twenty years, parallels the oxiranyl anion methodology. [3][4][5][6] Among the methods developed for the generation of aziridinyl anions are tin-lithium exchange in organotin aziridines, desulfinylation of sulfinyl aziridines, desilylation of silylaziridines, and deprotonation of easily available parent aziridines. 4e Of these, the deprotonation of simple and easily available aziridines remains by far the most convenient and efficient method for generating α-aziridinyl anions.