This thesis deals with the catalytic asymmetric epoxidation of alkenes mediated by chiral iminium salt catalysts. The first chapter contains a review of some of the most effective catalytic asymmetric methods for preparing chiral epoxides from alkenes. Merits and drawbacks of these methods are also highlighted where appropriate. The second chapter describes our efforts to design and synthesize chiral iminium salts as catalysts for asymmetric epoxidation of alkenes using oxone as the stoichiometric oxidant. The first part of this chapter describes the initial attempts to prepare a range of dihydroisoquinolinium salts, and led to the successful synthesis of one catalyst, which afforded up to 46% ee in the epoxidation of 1-phenyl-3,4-dihydronaphthalene.