Copper-exchanged zeolite Y (CuHY) is found to be a highly effective heterogeneous catalyst for the aziridination of alkenes using (N-(p-tolylsulfonyl)imino)phenyliodinane (PhI=NTs) as the nitrogen source: [GRAPHICS] Exchange of zeolite Y with other cations (Ag+, Co2+, Fe3+, Mg2+, Ni2+, Zn2+) was found to be ineffective and the yield of the aziridine was lower than that obtained if no catalyst was present. This is considered to be due to the ability of these metals to catalyze the breakdown of the PhI=NTs reagent into iodobenzene and toluene sulfonamide. Modification of the CuHY catalyst with bis(oxazolines) leads to the preparation of the first heterogeneous enantioselective aziridination catalyst and the results showing the effect of temperature and modifier concentration are described and discussed. The optimum reaction conditions for the aziridination of styrene are found to be using acetonitrile solvent at -10 degrees C with a Cu2+: bis(oxazoline) ratio of 2:1, and under these conditions, e.e. of 34-35% have been observed. The catalyst can be recovered and reused without significant loss of catalyst performance.