Microfinance (MF) has grown over the last two decades into an important sub-field of development studies. This special issue of Oxford Development Studies explores the contributions of MF, drawing particularly on research conducted in India. After a brief overview of the emergence of MF as a research field, this introduction develops three themes. First, we argue that MF interventions generally involve, and assume a process of transformation of, financially excluded people and groups who are not fully dominated by the logic of market exchange but have histories, culture, social relationships and politics structured by other kinds of authority and dynamics. Second, we argue that understanding MF interventions at the local level requires the social and political analysis of global development architecture, while MF may also play a role in consolidating or cementing global political economy at its base. Third, we argue that MF interventions have provided fertile ground for research into the causes and consequences of poverty. The introduction ends with summaries of the contents of the special issue.