This account deals with recent advances in the chemistry of magnesium carbenoids, especially new synthetic application, by using the electrophilic nature of magnesium carbenoids mainly reported from 2009 to present from our laboratory. Magnesium carbenoids, magnesium alkylidene carbenoids, cyclopropylmagnesium carbenoids, and cyclobutylmagnesium carbenoids were generated from aryl 1-chloroalkyl sulfoxides, aryl 1-chlorovinyl sulfoxides, 1-chlorocyclopropyl p
-tolyl sulfoxides, and 1-chlorocyclobutyl p
-tolyl sulfoxides, respectively, with a Grignard reagent at low temperature. The generated magnesium carbenoids were found to be stable at around −78 °C or higher at least 30 min. The reactions of the generated magnesium carbenoids with carbon- and heteroatom-nucleophiles resulted in the formation of many interesting products. These results offer new synthetic methods that are unprecedented and also lacking common sense. The essence of the reactivity and the structure of the magnesium carbenoids were investigated by DFT calculations.