This article reports on a study of volunteer levels of Catholics from various World regions who attended an international youth Catholic festival. Volunteering levels, types of volunteering, reason for volunteering, Catholic group membership and pro-social values are analysed. An online survey was administered five months after the Festival to 3413 English speaking attendees, aged 15-35. Interviews were conducted with 49 people prior to attending the festival. Follow-up interviews were conducted with 36 participants shortly after the Festival. Volunteering level was related significantly to Catholic group membership and pro-social values. Those who volunteered for social concern reasons undertook more volunteer hours than who volunteered for self-oriented reasons. Results also illuminate the mechanisms through which membership of different types of Catholic groups relate to levels and type of volunteering, with those belonging to a "Helping" group undertaking more volunteer time than those belonging to a "Religious" or "Social" group. (Contains 4 tables and 3 notes.)