The object of research of this thesis is the Common European Framework (CEFR) and its levels of proficiency in foreign languages. The development of the CEFR by nearly 50 member countries of the European Council started in 1991. The CEFR reference scales have become an international landmark and currently provide guidelines for the formulation of language policies for teaching, learning and assessment in about 30 European languages, including English. Although the CEFR is also used in Brazil in preparatory programs and in different types of selection processes, little is known about it and the literature on the subject in Portuguese is still scarce. The general aim of this study is to investigate which language theories were used in preparing the CEFR. Our specific aim is to analyze the concepts of language, teaching, learning, self and assessment in the CEFR to understand how its proficiency levels were determined. By means of a bibliographical research, several publications of the European Council,
partner institutions and independent researchers were gathered and organized to investigate the questions proposed in this research. In the end, it was possible to establish the historical evolution of the theoretical basis of the CEFR, its origins in the Linguistic Turn, with later developments from the School of Philosophy of Language
and the disciplines of Sociolinguistics and Pragmatics. The different concepts, especially the concept of language in the CEFR, were also duly considered. Finally, it was possible to understand more clearly how the said proficiency levels were determined.
