This paper develops a general framework for the analysis of marketing margins and the food system. It extends previous work by: (i) disaggregating farm-level production, food processing and food wholesale/retail activities, (ii) introducing closure with respect to factor markets and the rest of the economy, and (iii) introducing closure with respect to production and consumption in other regions. An analysis of the impact of income growth on the farm-retail price spread is shown to be dependent on the source of the income growth