Welfare and social care agencies rely on significant numbers of volunteers. We still know relatively little about why individuals volunteer, or why they volunteer for particular causes and in particular settings. This chapter outlines the existing literature and research on volunteering, discussing problems of defining and measuring unpaid and voluntary work, the history of and changes in volunteering, and the explanations offered for the motivations of those who volunteer. Data from an empirical case study of rape crisis centres and women's refuges are then used to assess the merits of existing literature in explaining volunteering in this setting.