Asymmetric syntheses of six-membered ring heterocycles are important research targets not only in synthetic organic chemistry but also in pharmaceuticals. The [3+3]-cycloaddition methodology is a complementary strategy to [4+2] cycloaddition for the synthesis of heterocyclic compounds. Recent progress in [3+3]-cycloaddition processes provide powerful asymmetric methodologies for the construction of six-membered ring heterocycles with one to three heteroatoms in the ring. In this account, synthetic efforts during the past five years toward the synthesis of enantioenriched six-membered ring heterocycles through asymmetric [3+3] cycloaddition are reported. Asymmetric organocatalysis uses chiral amines, thioureas, phosphoric acids, or NHC catalysis to achieve high enantiocontrol. Transition-metal catalysts used as chiral Lewis acids to activate a dipolar species is an alternative approach. The most recent advance, chiral transition-metal-catalyzed reactions of enoldiazo compounds, has contributed toward the versatile and highly selective synthesis of six-membered heterocyclic compounds.1 Introduction2 Asymmetric Formal [3+3]-Cycloaddition Reactions by Organocatalysis2.1 By Amino-Catalysis2.2 By N-Heterocyclic Carbenes2.3 By Bifunctional Tertiary Amine-thioureas2.4 By Chiral Phosphoric Acids3 Asymmetric Formal [3+3]-Cycloaddition Reactions by Transition-Metal Catalysis3.1 Copper Catalysis3.2 Other Transition-Metal Catalysis4 Asymmetric [3+3]-Cycloaddition Reactions of Enoldiazo Compounds4.1 Asymmetric [3+3]-Cycloaddition Reactions of Nitrones with Electrophilic Metallo-enolcarbene Intermediates4.2 Dearomatization in Asymmetric [3+3]-Cycloaddition Reactions of Enoldiazoacetates4.3 Asymmetric Stepwise [3+3]-Cycloaddition Reaction of Enoldiazoacetates with Hydrazones5 Summary and Outlook