Bilingualism has given rise to significant changes in Spanish-speaking countries. In the US, the increasing importance of Spanish has engendered an English-only movement; in Peru, contact between Spanish and Quechua has brought about language change; and in Iberia, speakers of Basque, Galician and Catalan have made their languages a compulsory part of school curricula and local government. This book provides an introduction to bilingualism in the Spanish-speaking world, looking at topics such as language contact, bilingual societies, bilingualism in schools, code-switching, language transfer, the emergence of new varieties of Spanish, and language choice - and how all of these phenomena affect the linguistic and cognitive development of the speaker. Using examples and case studies drawn primarily from Spanish/English bilinguals in the US, Spanish/Quechua bilinguals in Peru and Spanish/Basque bilinguals in Spain, it provides diverse perspectives on the experience of being bilingual in distinct cultural, political and socioeconomic contexts.