Crop diversification is an important policy objective to promote climate change adaptation, yet the drivers and impacts of crop diversification vary considerably depending on the specific combinations of crops a farmer grows. This paper examines adoption determinants of seven different cropping systems in Malawi, Zambia and Mozambique, and the impact of their adoption on maize productivity and income volatility – using a multinomial endogenous treatment effect model. These cropping systems consist in different combinations of four categories of crops: dominate staple (maize), alternative staples, legumes, and cash-crops. The study finds that relative to maize mono-cropping systems, the vast majority of systems have either neutral or positive effects on maize productivity, and either reduce or have neutral effects on crop income volatility. In particular, cropping systems that include legumes produce better outcome in most cases than those that feature cash crops. From a policy perspective, three recurrent determinants of diversification are found. First, private sector output market access is an important driver of diversification out of maize mono-cropping. Policies crowding in private output market actors can help to promote a wide range of more diverse cropping systems. Second, proximity to public marketing board buying depots discourages the adoption of more diverse cropping systems. Therefore, reforms to these institutions must be part of any diversification strategy. Finally, in all countries and for all systems, land size is a key determinant of adopting more diverse systems. Thus, land policy is an integral element of any boarder diversification strategy.