Onobrychis viciifolia (sainfoin) is a forage legume crop with many positive agronomic, environmental, nutritional and nutraceutical attributes. Farmers also benefit from its drought tolerance in areas of low rainfall and light free draining soil, mainly due to its deep taproot. It is resistant to most common pest and diseases and is a valuable resource for pollinators, specifically cultivated for honey production in some regions. It has many benefits for animals, being highly palatable and without danger of bloat, which can be life-threatening to livestock. Its decline in Northern Europe started during the Green Revolution and was impacted by changes towards more intensive farming. Unlike other forage legume crops such as red clover and lucerne, sainfoin does not respond well to inputs and is difficult to establish and maintain. Sainfoin could be classified as an ‘orphan crop’ with very little genetic improvement or agronomic studies in the past 60 years. In the past 5–10 years, however, there has been a resurgence in interest and this has given rise to a number of studies and initiation of systematic improvement of the crop, which is indispensable to its reintroduction into the farmed environment. Interest has been driven in part by considerable evidence to suggest that condensed tannins present in the legume foliage, together with other polyphenol compounds, have positive effects on animal nutrition together with anthelmintic properties. These compounds are also thought to play a role in environmental benefits. There remain many challenges to address in order to optimize the potential for cultivation of sainfoin and its use as a beneficial forage crop. This review makes particular reference to a recently completed project; ‘Legume Plus’, funded by the European Union and embracing a multi-disciplinary approach to both understand and improve the crop for farmers. The present review covers results from both this project and other studies during the past 5 years, also drawing on historic studies of etymology, taxonomy, genetics, agronomy and botany, aiming to be a useful resource for research and for practical plant breeders and agronomists.