This article presents an overview of the literature relating to the effects of the Content and Language Integrated Learning (CLIL) approach on the process of language and content acquisition. The overview is divided into five sections and the effects of CLIL on the students’ language system is described according to four language skills (reading, writing, speaking and listening, vocabulary and grammar). It is stated that while CLIL leads to a general improvement in relation to language proficiency, there are also some observations proving that certain language areas (e.g. syntax, pragmatics) are unaffected.