Yield-enhancing agricultural technologies, like improved crop varieties, are widely promoted in developing countries to improve the food security, income, and welfare of farm households. Nonetheless, farm households show low adoption rates of these technologies. To gain more insight into the drivers of and the barriers to the adoption of improved crop varieties, we study the adoption of improved sunflower varieties by smallholder farmers in Tanzania. Unlike most earlier studies, we distinguish between the initial adoption and the extent of adoption. Additionally, we investigate the roles of market constraints and liquidity constraints, which are largely ignored in previous adoption studies. We find that risk aversion and liquidity constraints are barriers to adoption, whilst radios and extension service are important information channels for new technologies. Our results can help to improve policies, development programmes, and business decisions and finally to enhance agricultural productivity and farm household welfare.