In the last two decades knowledge on volunteering has significantly expanded, but a thorough understanding of the organizational socialization of volunteers is still lacking: the process through which one learns the job, internalizes organizational values and goals, and becomes an effective and involved volunteer. By performing an ethnographic study with Israeli volunteers working for at-risk youth, the organizational process was portrayed. The Volunteering Stages and Transitions Model (VSTM) presented in this article indicates five different phases in volunteers' socialization (nominee, newcomer, emotional involvement, established volunteering and retiring). The importance of the model lies in the way it explains transitions between the phases and details the process, experiences, and emotions involved in each phase. The transformation is reflected in different aspects related to volunteer work: activity and training; emotions and perceptions; attitudes and behavior; perceived benefits and costs; and relationships with the organization, peers and recipients.