Cadmium is a group 12 transition metal known for its use in coordination and organometallic chemistry, though its toxic nature limits its application in modern catalysis. Historically, cadmium salts such as cadmium acetate and cadmium chloride have been used as Lewis acids to activate carbonyl and unsaturated substrates in organic reactions. Organo-cadmium reagents, particularly dialkylcadmiums, were once employed in nucleophilic additions to acid chlorides to selectively form ketones without over-addition to tertiary alcohols—unlike Grignard or organolithium reagents. However, due to their toxicity and the availability of less hazardous alternatives, their synthetic use has significantly declined. In materials science, cadmium compounds such as cadmium selenide (CdSe) play essential roles as semiconducting components in quantum dots used in optoelectronic devices and photovoltaics. Despite limited application in green chemistry and modern catalysis, cadmium’s unique reactivity in certain contexts—especially as part of solid-state catalysts and nanomaterials—continues to find niche applications in sensor technology and electronic materials.