This case study investigates the criteria used by English teachers to select textbooks for Educación Secundaria Básica (ESB) in state-run schools in the district of La Matanza, Province of Buenos Aires. The study was motivated by the increasing diversity of teachers’ educational backgrounds following the implementation of the Federal Education Law and the need to determine whether textbook selection is based on scientifically supported criteria within the framework of Communicative Language Teaching (CLT). A descriptive and exploratory case-study design combining qualitative and quantitative approaches was adopted. Data were collected through surveys administered to English teachers and analyzed using descriptive statistics and qualitative interpretation. The literature review drew on the work of Cunningsworth, Cunningham, Harmer, Littlejohn, Richards and Rodgers, and Ur to establish a theoretical framework for textbook evaluation and selection. The findings indicate that teachers primarily select textbooks according to students’ needs, cultural background, content, and affordability. However, textbook choice is also strongly influenced by publishers’ representatives, catalogues, and the availability of complimentary copies, while systematic evaluation procedures recommended in the literature are only partially applied. The study also identifies inconsistencies between teachers’ stated beliefs regarding methodological principles and their actual textbook selection practices. It concludes that economic constraints and contextual realities significantly shape decision-making. Finally, the research proposes a revised survey instrument and offers recommendations to promote more systematic, research-informed textbook selection practices that better support language learning outcomes in public secondary education.