This chapter is concerned with the reduction and related reactions of α,β-unsaturated ketones by alkali and alkaline earth metals in liquid ammonia. Upon treatment with a metal in liquid ammonia (usually containing an ether co-solvent) a simple alpha, beta-unsaturated ketone is converted into the metal enolate corresponding to the saturated ketone. Research during the first half of the 20th Century revealed that a variety of organic compounds undergo reduction with metals in liquid ammonia but preparative metal-ammonia reductions of α,β-unsaturated carbonyl compounds were apparently not described until 1951. In addition to affording a remarkable degree of stereoselectivity, many metal-ammonia reductions of unsaturated carbonyl systems can be preformed in a variety of functional and protective groupings and the reaction is generally free of the rearrangements sometimes observed when chemical reduction methods are used. The unique features of metal-ammonia reductions and related reaction have led to their wide application in total synthesis and transformations.