The key role of institutions in mediating rural markets, and thus in influencing economic change in agriculture, is explored. Pertinent theories of institutional change are reviewed and the place of external intervention, whereby outside agencies attempt to assist market mediation, is examined. The institutional cases of plantations and smallholdings in tree crop agriculture are scrutinised, and their respective performances are compared with a focus on market failures. The case of traditional land rights is investigated in similar vein. The analyses indicate that government interventions to remedy market failures may be helpful in improving information, capital, land, and output markets, but should be carefully designed to match economic and social circumstances. The economics of institutional change is shown to be a vital sphere, deserving further consideration.