Rental markets for agricultural land in communal areas of Southern Africa are often constrained, despite potential benefits for many households. High transaction costs and insecure tenure have precluded active rental markets in the region. The notion that conditions necessary for land rental will emerge in response to increasing population pressure and better prospects in farming is questioned. Attention is focused on interest groups opposed to changes in customary tenure, and policies designed to 'supply the institutional changes needed to support an active rental market. The main conclusion is that farmer support programmes are unlikely to realise their full potential unless they are accompanied by adaptive strategies that make endogenous changes in customary tenure more predictable.