This study aimed to identify how the teachers’ beliefs about Content and Language Integrated Learning (CLIL) affect the way they implement the CLIL approach in their classrooms. This qualitative case study on teachers’ beliefs and CLIL combines interviews and class observations. The study focuses on two Colombian educators who teach subject contents and English as a foreign language at the university level. The results of the present study confirm that in spite of the fact that teachers know some basic notions of the CLIL approach, many relevant CLIL aspects were absent during their teaching practice. Thus, this study suggests that the participant-teachers’ beliefs about CLIL are insufficient to implement a successful CLIL lesson. For this reason, a training development program is recommended in order to improve pedagogical actions in the CLIL classes taught in English for the teachers at this institution.