III Colloquium on Semi-Immersion in Catalonia ; III Encuentro sobre Semi-Inmersión en Cataluña ; Since 1998, CLIL is an official learning and teaching approach for primary schools in French-speaking Belgium. In 2001 a number of Dutch-speaking schools in Brussels followed this example. This paper traces the practice of CLIL in these two areas and discusses a number of research issues. In the first part the political issues regarding the implementation of CLIL are addressed. It is shown how feelings toward this approach differ throughout the country and why this is the case. In the second part, the practice of CLIL is examined. A number of schools teach as much as 70% of the curriculum in the target language, while others limit themselves to 20%. The didactic consequences of the different approaches are examined. Among the problems addressed are the questions (1) whether it is desirable or not that in the development of pupils' linguistic skills, at a certain point in their development, the target language turns out to be the best language? and (2) whether or not it is desirable that reading starts in the target language rather than in the first one? In the third part the six tenets used by our research group are discussed. These are: (1) knowledge of the target language, (2) knowledge of the mother tongue, (3) knowledge of subject-matter, (4) attitudes and motivation, (5) cognitive development and (6) neuroscientific aspects of the brain of bilinguals. The results indicate that CLIL is a powerful learning approach that goes far beyond language knowledge and development but reaches out to cognitive and neuroscientific aspects as well. This leads us to think of CLIL as a really innovative approach not only to language education but to education in general.