This quantitative research focuses on exploring and describing the beliefs of 418 in-service teachers on language teaching approaches and multilingualism in the South of the Basque Country. The findings report key factors and features of multilingual education in the region where Basque (minority language), Spanish (majority language), English (first foreign language) and French (second foreign language) are integrated in the curriculum. Results indicate that teachers' views about language teaching approaches are in line with current trends and theories about multilingual language teaching methodologies. The ANOVA results highlight the significant influence of two variables, in-service teachers' self-reported L3 (English) proficiency level and the teaching through their L3, on the development of these beliefs. Implications of this study may help to better understand the importance of developing and implementing specifically designed courses based on multilingual language teaching approaches to exploit the existing in-service teachers' favorable beliefs and therefore to materialize and adopt more vanguard multilingual teaching practices that may boost language learning.