This chapter gives a concise overview of research results with regard to immersion teaching in preschool and primary school. After disentangling some terminological issues concerning, notably, the usage of the terms immersion and CLIL, the authors go on to discuss different forms of immersion programs, results of L2 attainment, content learning, competence in the L1, cognitive skills, and the attainment of so-called at-risk learners. In the second part of the chapter, practical, methodological and didactic considerations for the implementation of immersion programs are discussed. The authors conclude with making a case for intensive bilingual education.