This article explores the ways in which volunteering for development is changing in the context of the shifting wider ecology of international development. It draws on a two-year, action research project into the value of volunteering undertaken by volunteer researchers in Kenya, Mozambique, Nepal and the Philippines. The article frames this research and the articles in this IDS Bulletin in the key debates – past, current and emerging – around the role, identity and value of volunteers in development processes. It identifies critical characteristics of effective volunteering for development as: the insider–outsider relationship; participatory processes, long-term programming; and a sustained focus on the poorest and most marginalised. The authors draw attention to the relevance of volunteering to achieving the Sustainable Development Goals (SDGs), and call for better understanding of indigenous informal volunteering and how ‘outsider’ volunteers can support it.