The main objective of this study is to identify criteria that would allow us to determine when a collection of people is a group. A bibliographic search of the psychological literature has yielded the terms groupness, entitativity, and groupality. These three constructs are then theoretically analyzed and compared, and are found to share two main aspects: (a) the conception of groups as a continuum varying in their level of group development (LGD) and (b) most of the central criteria that have been considered to define a group as a group. Regarding these central criteria, we categorize them as determining elements, LGD criteria, and group results trying to respect their different epistemological positions. The theoretical proposal outlined here provides a basis on which to develop tools that will enrich organizational assessment.