Do we sound different when we speak a foreign language? This book presents the results of a study dedicated to answering this question. When we speak, our voice carries a lot of information in addition to the linguistic content of what we want to communicate. So when we speak a foreign language, compared to our mother tongue, we can change our voices, even if unconsciously. This study sought to verify differences between the voices of bilingual Brazilian speakers when speaking English compared to Portuguese. It also investigated whether possible voice changes were perceptually detected by listeners who were also Brazilian and bilingual. The results showed that some speakers have quite distinct characteristics between the languages and that many of these differences are perceived by listeners.