Activated cyclopropanes, such as vinyl and carbonyl cyclopropanes, are useful building blocks in organic chemistry due to their exceptional reactivity. This review focuses on the use of cyclopropyl carbonyls and imines in cyclization and cycloaddition reactions for the synthesis of cyclic compounds. Cycloisomerization and other cyclization reactions are treated first, followed by formal cycloaddition reactions and applications in total synthesis. For each class of reactions, key pioneering works are shortly presented and emphasis is then set on recent results. Indeed, the utility of activated cyclopropanes in organic synthesis have been significantly increased in the last years by combining modern catalytic methods with the well-established reactivity of these building blocks. Together with progress in the synthesis of the cyclopropanes, these new methods allowed a better control over the diastereoselectivity and enantioselectivity of the reactions as well as their use for the synthesis of complex natural products.