Existing studies indicate that teachers beliefs are a window toward understanding pedagogical practices. If we investigate these beliefs and uncover their roots, perhaps we may be better equipped to understand teachers decisionmaking processes. This dissertation sets out to investigate the beliefs of a teacher of English as a foreign language in a public school in Rio de Janeiro, their relation to pedagogical practices and identity processes, and their stability. Following a case study methodology, we gathered data by observing 10 classes and interviewing the teacher. The data were analyzed quantitatively and qualitatively. Results revealed that the teacher s belief system about language learning and teaching began to be formed when she was only an EFLer and that it has been polished by teaching experience, continuing education and postgraduate courses. However, the system has remained relatively stable. In a nutshell, results show that the teacher s practice bears a symbiotic relationship with her belief system, which gives practice its shape and at the same time is shaped by practice.