Although previous research suggests that connection to large, mostly anonymous groups is important for the fulfillment of psychological needs and a sense of psychological well-being, no measure exists to assess individual differences in this area. In 5 studies, we developed and provided support for the validity of the Tendency for Effervescent Assembly Measure (TEAM). Utilizing data from student and community samples, we conducted exploratory factor analyses to guide item selection for the scale (Study 1), evaluated the structure of the scale in an independent sample (Study 2), examined the convergent, discriminant, and incremental validity of the scale (Study 3), and assessed measurement invariance of the scale across different demographic groups (Study 4). Study 5 explored the role of social needs fulfillment in effervescent assembly, as well as examined the relationship of the scale with recent collective effervescence experiences. Results revealed that our final 11-item scale was unidimensional, with excellent internal consistency and good test-retest reliability over 2 months. Measurement invariance was established across gender, ethnicity, and religion, providing support for the validity of the measure across demographic subgroups. Importantly, the TEAM predicted decreased loneliness, increased positive feelings, a sense of meaning in one's life, self-awareness, and spiritual transcendence, above and beyond the effects of the big 5 factors of personality and collective and relational interdependence. Furthermore, results suggested that positive outcomes associated with the TEAM are because of social need fulfillment.