In the past three decades, volunteers became the backbone of many human service organizations (HSOs). We propose that the role of groups in volunteer management is often neglected. We first review the theoretical and empirical literature on group dynamics relevant to fostering volunteering, followed by a literature review on the nexus between groups and volunteering. We then develop a model of four volunteer group types and their unique utility as it pertains to volunteering in HSOs: habitual volunteering group, dual-identity group, training-induced group, and provisional group. We conclude with a summary, discussion, and implications regarding the role of groups in volunteer recruitment, socialization, motivation, and retention.