Common bean ( Phaseolus vulgaris
L.) is an important crop mainly for smallholder farmers in Tanzania, for home consumption and cash income. Its productivity has been low due to a number of factors, including environmental stresses and limited input use. The socio-economic environment calls for development and dissemination of improved bean varieties that are well adapted to multiple constraints, in order to improve and stabilise bean productivity on smallholder farms. The objective of this study was to assess the adoption and spatial distribution of improved common bean varieties in Southern Highlands of Tanzania. The study used a bivariate probit model to account for possible correlation between the disturbances. Results show that the improved varieties have extensively diffused in the study area, with new improved bean varieties replacing old ones. A host of factors at plot level (e.g. perceptions about soil fertility status and plot distance from residence), household level (e.g. agricultural wealth, number of dependents, access to off farm income and years of experience in bean growing), and village level (e.g. distance from the village to main road, agricultural credit), significantly influenced the adoption of the improved varieties. Farmers who adopted new improved varieties attached a higher weight to agronomic attributes. Market attributes partly explained continued cultivating of old improved bean varieties. Results support investment in market hard and soft infrastructure in form of roads, financial services, farmer cooperatives and integration of ICT in seed dissemination.