Content and Language Integrated Learning (CLIL) has become increasingly popular over the past decade in language teaching. This paper probes into the effectiveness of the CLIL approach in Greek EFL classrooms in boosting learners’ language learning, subject knowledge and academic achievement. A qualitative methodology was employed, including interviews which enabled the collection of qualitative data. The sample comprised primary and secondary education teachers in Greece, a European country where CLIL has been implemented in some schools. The findings indicate that CLIL has a positive effect on learners’ motivation and engagement and can lead to significant gains in language achievement and subject content knowledge. The paper also highlights some challenges to successful implementation such as teachers’ language skills and the need for appropriate materialsand resources and concludes with suggestions for future research in this field as well as some suggestions for the improvement of CLIL implementation.