The historical spread of Spanish and Portuguese throughout the world provides a rich source of data for linguists studying how languages evolve and change. This volume analyses the development of Portuguese and Spanish from Latin and their subsequent transformation into several non-standard varieties. These varieties include Portuguese- and Spanish-based creoles, Bozal Spanish and Chinese Coolie Spanish in Cuba, Chinese Immigrant Spanish, Andean Spanish, and Barranquenho, a Portuguese variety on the Portugal-Spain border. Clancy Clements demonstrates that grammar formation not only takes place in parent-to-child communication, but also, importantly, in adult-to-adult communication. He argues that cultural identity is also an important factor in language formation and maintenance, especially in the cases of Portuguese, Castilian, and Barranquenho. More generally, the contact varieties of Portuguese and Spanish have been shaped by demographics, by prestige, as well as by linguistic input, general cognitive abilities and limitations, and by the dynamics of speech community.