Content and Language Integrated Learning (CLIL) has now become a feature of education in Europe from primary school to university level. CLIL programmes are intended to integrate language and content learning in a process of mutual enrichment. Yet there is little consensus as to how this is to be achieved, or how the outcomes of such programmes should be measured. It is evident that a further type of integration is required: that of bringing the practice of CLIL into closer contact with the theory. In this, it is necessary to establish the role played by other fundamental aspects of the...