The purpose of this chapter is twofold: to address the concept of England’s far north as a frontier and to examine corresponding ideas about the spatial environment of the region. On the one hand, the problem is to address what this means for our historical understandings today; on the other, it demands also that we explore what this meant for the later middle ages. If militarisation is often understood to be a feature of medieval frontier societies generally, then it is a matter which we shall touch on only briefly here; the topic will be picked up again in subsequent chapters. To the forefront of the agenda now comes a scrutiny of the ideas we bring to the subject and an examination of the ways in which the medieval frontier could be ambivalent: both clear and ambiguous, and at once static and dynamic.