This essay argues that the central concept for analysis of agrarian social relations is the form of production. This is conceived through a double specification of the unit of production and the social formation. The approach allows for the analytical specification of simple commodity production and capitalist relations of production in a manner consistent with the development of new concepts within political economy for agrarian structures which do not correspond to modes of production. The latter have generally been referred to as ‘peasant’, a term derived through empirical generalisation and resting on a (usually) implicit contrast with simple commodity production. The contrast can be made more rigorous through the concept of commoditisation, defined as the penetration into reproduction of commodity relations. Simple commodity production is a concept within political economy, allowing for deduction of conditions of reproduction and class relations. ‘Peasant production is negatively defined as resisting commoditisation, and nothing can be deduced about reproduction or class relations. ‘Peasant’ must be replaced ty a comprehensive and mutually exclusive set of rigorously defined concepts specifying forms of production. Procedures for defining such forms of production are suggested.