The growing interest in greater farmer participation in formal agricultural research has had major implications both for investment priorities and for models of organisation, implementation and management of agricutural research and development. The authors of this work identify, characterise and contextualise the experimental activities undertaken by farmers themselves, providing a theoretical and empirical base from which alternative models for the interaction of formal research and farmers' experiments can be evaluated. It is a seminal contribution to the debate among donors and development agencies, as well as in academic circles, about the search for more socially and economically acceptable models for the development and transfer of agricultural technology.