Middle English is traditionally thought of as the “dialectal phase” of English: the period when dialectal variation is reflected in the written record. There is general agreement that the written variation is to a large extent geographically conditioned: however, what precisely it reflects and how it relates to the physical map are remarkably controversial questions. Approaches to dialectal variation have changed dramatically over the last century, as have attitudes to written language; however, the implications of such changes may take a long time to permeate scholarly traditions. This chapter reviews some of these major changes and discusses their implications for the study of Middle English variation. It argues that there can be no single absolute relationship between linguistic form and geography: rather, there are numerous ways of relating the two, and consequently innumerable different dialect maps. Middle English dialects, accordingly, emerge from the data: whether as constellations shaped by the questions we ask or as observational artifacts based on our subjective experience.