Conservation agriculture (CA) involves the practice of three interlinked principles of minimum soil disturbance, a permanent soil cover and crop rotation. Despite the many stated benefits of the technology, its uptake in Africa has been slow. This study applies the theory of planned behaviour to investigate the attitudes, the role of the social system (social influence, by-laws and customs) and the institutional environment in the decision to practice CA principles and on the area under CA in Choma, Zambia and Nkayi, Zimbabwe. The study finds differing attitudes between districts towards CA outcomes. Local by-laws have a positive correlation with the practice of minimum soil disturbance but negative correlations with the practice of soil cover and crop rotation. Social influence and customs have significant relationships with the area under CA. Institutional support is perceived to be necessary for the practice of minimum soil disturbance but not so for the practice of crop rotation or on the area under CA. We conclude that the attitudes towards CA depend on the performance of the CA options promoted to farmers while the effects of the social system components and institutional factors on the uptake of CA depends on how the particular CA principle fits into the social and institutional environment in which it is promoted. We recommend agriculture extension services and policymakers to pay more attention to these issues in the promotion of CA.