The self-concept is dynamic, with momentary definition shifting from a representation of self as a unique and independent social agent to an undifferentiated and interchangeable group member. Indeed, the individual self and collective self are fundamental components of the self-concept, with each being important and meaningful to human experience. However, are those selves equally important and meaningful? We review a program of research empirically testing three competing hypotheses that suggests that the motivational core of human experience is (a) the individual self, (b) the collective self, or (c) determined by contextual factors that make a given self momentarily accessible. The research furnished unanimous and consistent evidence that the individual self is the motivationally primary form of self-definition.