This Element introduces the Disambiguating Project (DP) about the units of selection. By DP, the authors mean the thesis that the expression 'units of selection' refers to at least three non-co-extensional functional concepts: interactor, replicator/reproducer/reconstitutor, and manifestor of adaptation/type-1 agent. They present each concept and demonstrate the necessity of their isolation, because each of them responds to a distinct question about...