A number of examples of addition and polymerization reactions is presented with special emphasis on the chemical behaviors of activated monomers and/or activated nucleophilic reagents. Lithium alkoxyethanolate forms a complex with lithium alkyl. Spectroscopic studies showed this complex to possess agent-separated ion pairs. The nature of the complex is characterized by the enhanced reactivity of styrene in the copolymerization reaction with butadiene initiated by the complex. Magnesium alkyl can be sufficiently activated by magnesium alkoxyethanolate to polymerize styrene and diene. Aluminum alkyl and zinc alkyl are able to induce the anionic polymerization of vinyl ketones, but not of unsaturated esters or nitriles. Aluminum or zinc alkoxyethanolates fail to activate their corresponding metal alkyls. Bipyridyl, sparteine, triphenylphosphine, HMPT, and related Lewis bases, however, activate aluminum alkyl enough to react with carbon-carbon double bonds of the unsaturated esters and nitriles. Crotononitrile can be polymerized by the AIR3-HMPT system to form a colorless polymer, where possible side reactions between CN and AIR3are prevented by HMPT. Mutual activation through complex formation is confirmed by a model system of a vinyl ketone with organozinc compounds. AIR3-HMPT does not polymerize vinyl ketones because of a lack of complex formation. N-Carboxy-α-alanine anhydride (NCA) can be polymerized with zinc alkyl as initiator. The formation of activated NCA by proton abstraction from the NH group is shown to be the essential stage for polymerization. Zinc alkyl is also activated by conventional acid anhydrides. The propylene oxide ring can be cleaved with the ZnR2-phthalic anhydride system, which is the initiation step in the alternate copolymerization between propylene oxide and the acid anhydride. The propagation mechanism of the CO2-epoxide copolymerization is also discussed.