Methods of linguistic data collection are among the most central aspects in empirical linguistics. While written questionnaires have only played a minor role in the field of social dialectology, the study of regional and social variation, the last decade has seen a methodological revival. This book is the first monograph-length account on written questionnaires in more than 60 years. It reconnects – for the newcomer and the more seasoned empirical linguist alike – the older questionnaire tradition, last given serious treatment in the 1950s, with the more recent instantiations, reincarnations and new developments in an up-to-date, near-comprehensive account. A disciplinary history of the method sets the scene for a discussion of essential theoretical aspects in dialectology and sociolinguistics.