*NEW EDITION* Since the inception of sociolinguistics more than three decades ago, the correlation of dependent linguistic variables with independent social variables has provided the theoretical core of the discipline. Chambers reviews the essential findings of Henrietta Cedegren, William Labov, Lesley Milroy and James Milroy, David Sankoff, Gillian Sankoff, Peter Trudgill, Walt Wolfram, and many others, and puts them into context both with the work of the numerous linguists who have followed their lead and with their intellectual forbears from Wilhelm von Humboldt and Louis Gauchat to Edward Sapir.