This book historically locates general sociolinguistics, points out sociolinguistic lines of research, considers the state-of-the-art in the Catalan speaking countries and presents an application of the authors' view and method of language variation to the study of Petrer, a municipal area in Valéncia. It integrates the idea that languages are important symbols of identity and the idea that formal understanding of language structure and use causes a better understanding of the nature of language(s).