Experiments in bilingual education in Europe increasingly appear under the abbreviation "CLIL" (Content and Language Integrated Learning). The main concept in it seems to be that of integration, as yet little described in research and insufficiently made conscious and explicit in the teaching process. This paper aims at studying the modes of integration between language and content by identifying different types of knowledge at the crossroads between the linguistic paradigm and the subject paradigm. It is based on discourse and interaction analysis of classroom interaction sequences in various subjects. It proposes elements for a basic theoretical framework designed to sustain the view of CLIL as an alternative not only in second language didactics, but also in the didactics of non-linguistic subjects.