This book reports the results of a study which investigated the relationship between the perception and production of English vowels by 18 highly proficient Brazilian EFL speakers. Two experiments were carried out: A production test to measure the first two formants and duration of the learners'' English and Brazilian Portuguese (BP) vowels, and an identification test with synthetic stimuli to investigate the L2 (second language) perception of English vowels. The production and perception results reveal that the Euclidean distance between the three English target pairs (/i-I/, /E-ae/, /U- u/) was significantly larger for the American English monolinguals than for the L2 learners, thus indicating that the Brazilians have difficulty in both producing and perceiving these vowels in a native-like fashion. Importantly, some relationship between vowel perception and production was found because the target pairs which were better perceived were also the ones produced more accurately by the L2 learners. These results provide further evidence for the fact that L2 perception outperforms L2 production.