People use social categories to perceive and interact with the social world. Different categorizations often share similar cognitive, affective and behavioral features. This leads to a hypothesis of the common representational forms of social categorization. Studies in social categorization often use the terms “ingroup” and “outgroup” without clear conceptualization of the terms. I argue that the ingroup/outgroup distinction should be treated as an elementary relational ego-centric form of social categorization based on specific cognitive mechanisms. Such an abstract relational form should produce specific effects irrespective of the nature of a particular social category. The article discusses theoretical grounds for this hypothesis as well as empirical evidence from behavioral and brain research. It is argued that what is commonly termed as “ingroup” and “outgroup” can be produced by distinct cognitive operations based on similarity assessment and coalitional computation.