In revising this textbook, we have taken pains to retain the features that have made it a staple for linguists and students for eighteen years. Dialectology presents the fundamentals of studying language variation between and within communities. More than one reviewer of the first edition noted that ours was the first book to survey those fundamentals although dialect studies have been pursued systematically for about a century and a half. For this second edition, one of the topics most in need of updating was dialect geography, which had lost much of its impetus in the decades before our first edition but has since been revitalised. Partly this revitalisation is mechanical, stemming from technological advances in the handling of large databases, but partly it is theoretical, resulting from increased representativeness in sample populations and closer attention to the social dynamics of diffusion and change. Our integration of socio-linguistics with more venerable traditions as a highly influential new branch of urban dialectology surprised a few readers but was generally received as an interesting innovation. Now it would be shocking, and hopelessly muddled, if someone tried to keep them apart.