This chapter reviews methods for the generation of halocarbenes and the reaction of the latter with unsaturated substrates. Chemical transformations of the derived halocyclopropanes are discussed in sufficient detail to demonstrate the synthetic utility of this class. The formation of dihalocyclopropanes from dihalocarbenes was first accomplished in 1954 by Doering and Hoffmann who used chloroform t- butoxide to generate the dichlorocarbene. Since that time a variety of other methods have been developed for the generation of halocarbenes. The various methods are discussed.