Chapter 3 examines the origins of modern territoriality in settler colonies, centring on the English colonies of North America. A range of existing accounts view property as important in the history of sovereignty. This chapter engages with them, offering an account of how property surveying drove the emergence of modern territoriality in North America. A host of settler colonial conditions, ranging from cultural understandings of property to non-recognition of Native American boundaries, resulted in the use of geometric surveying techniques in the creation of private property becoming central to colonial life. Territorial disputes between colonies were then addressed using boundary-making techniques of delimitation and demarcation already familiar from the resolution of property disputes. After US independence, these techniques were used to create interimperial boundaries. Comparisons between different types of settler colonialisms globally are used to add weight to this explanation and to justify the focus on English North American colonies.