Abstract:The quantitative impact assessment of microfinance programmes, like the programmes themselves, originated in Bangladesh. This essay reflects on the significance and usefulness for present day researchers of the analytical advances made in Bangladesh since the beginning of the 1990s. Particularly in the area of selection bias, fungibility and the assessment of wider impacts, it argues, those advances are crucial, and need to be borne in mind by all practitioners; but financial sustainability remains an unresolved problem.