This review encompasses syntheses, characterizations, and applications of InP magic-sized clusters (MSCs) which are originally found as intermediates during the growth of InP quantum dots (QDs). Various tools to characterize MSCs and the intermediate characteristics of InP MSCs and InP MSCs having incorporated heterogeneous atoms such as chlorine or zinc are discussed. Developments in the syntheses of InP QDs and MSC-mediated growth mechanisms involving fragments, monomers or other nanoclusters are also addressed.