This article aims to classify social identity-based theories of intergroup differentiation in terms of different dimensions of social identity to understand further the motivational bases of intergroup differentiation. For this purpose, I attempt to incorporate three lines of research in social psychology: (a) theories examining intergroup differentiation as a function of social identity, namely social identity theory and SCT; (b) studies suggesting social identity as a multidimensional construct; and (c) motivational theories of intergroup differentiation, namely subjective uncertainty reduction theory, optimal distinctiveness theory, and self-esteem hypothesis. It is suggested that subjective uncertainty reduction theory explains motivational basis of cognitive dimension, that optimal distinctiveness theory explains motivational basis of emotional dimension, and that self-esteem hypothesis explains motivational basis of evaluative dimension of social identity. Finally, the relationships between motivations of intergroup differentiation as a function of different dimensions of social identity are considered.