Over the past two decades, there has been much scientific interest in the potential of agroforestry for small-scale farming. One form of agroforestry that has received particular attention is alley farming, intended as a sustainable, intensive system that would radically improve the long-term prospects of resource-poor farmers. Although impossible to estimate precisely, total global expenditure on alley farming research, development and promotion to date runs to tens of millions of US dollars. It is now widely recognised that the technology has far less potential than originally anticipated, major limitations having emerged in both its technical and socio-economic characteristics. This paper reviews the documented on-farm performance of alley farming to date, identifying niche areas with some prospects for successful adoption, and suggesting specific areas for further research.