The book presents an analysis of selected domains of morphosyntactic variation in a 250,000 word collection of the Middle English Paston Letters (1421-1503) from a historical sociolinguistic point of view. In the three case studies, two nominal and one verbal variable are described and discussed in detail: the replacement of Old English h-take, make, give, have, do plus deverbal noun). While the study aims at a balanced integration of theories and methods from a number of different approaches in sociolinguistics, cognitive linguistics, typology, and language change, its main focus is social network theory and the role of the linguistic individual in the formation and change of language structures. Questions of individual language use and of deliberate versus unmonitored changes in the (individual) system take center stage and are discussed in the light of social network analysis. Traditional empirical social network analysis is carefully revised. Despite its many merits in present-day sociolinguistics, it often needs to be supplemented by hermeneutic-biographical analyses of the individual speakers' lives when applied to historical data. With this background, common theories and models of language change, such as grammaticalization, paradigmatic pressure, typological alignment, and generational shifts, are illustrated and evaluated from the point of view of single speakers and social groups, and their particular embedding in the speech community through various network structures. The book is of interest to advanced students and researchers in English and general linguistics, Middle English, historical linguistics and language change, corpus linguistics, as well as sociolinguistics.