The purpose of this conceptual article is to further our understanding of how evolving volunteer trends impact on volunteering intensity. The aim is to provide clarity by applying to the volunteer literature a theoretical framework that can be adapted to different ways in which people volunteer and thus may inform subsequent empirical work. First, we address academic debates concerning the measurement of volunteer effort. Second, we propose using public service motivation (PSM) theory as a means to understand the motivation of volunteers across sectors. We suggest that different PSM dimensions may be more dominant in certain volunteer settings than others and incorporate person–organisation fit as a means to understand the relationship between PSM and volunteering intensity. Finally, this article proposes directions for future research.