In this paper, we study the evolution of agricultural product specialisation at farm and county level from 1979 to 1997 in Spain, thus covering all the stages of the gradual implementation of the Common Agricultural Policy. We use a multiproduct version of Theil and Finizza's index of segregation that allows us to decompose farm product specialisation into county specialisation with respect to the national level, i.e., the usual measure of regional specialisation, and farm specialisation within counties. Our results confirm the importance of increasing regional specialisation but also highlight that trends of farm specialisation within counties have varied across large agricultural areas. In particular, regions more specialised in export-oriented products seem to have speeded regional specialisation