An important component of comparative third sector research seeks to identify and explain differences in levels of volunteering in different countries. Sometimes the research draws on data collected in country-specific studies; sometimes researchers use the same survey instrument across several countries. A fundamental question that does not seem to have been asked is just what is volunteering and what should the surveys be trying to measure? Attempts to answer this question immediately become entangled in the two alternative paradigms: one which draws on economics and law and focuses on non-profit organisations, particularly charities; and one which draws on sociology and politics and is more interested in voluntary or mutual associations and civil society. This paper considers whether a single approach that meets the needs of researchers in both paradigms is possible.