How did the American state consolidate its power over the vast and remote territory of the western United States? This chapter orients readers to the period of western expansion spanning the 1860s to the early 1900s and the crucial, often unseen, role of the US Post within this project. It explains the book’s methodology of using a dataset of more than one hundred thousand post offices to map the spread of the western postal network, part of a larger approach of digital history. This spatial analysis leads to four findings about the US Post and its status as a “gossamer network”: that it was big, spatially expansive, fast moving, and ephemeral. The chapter then introduces the concept of the agency model, a new organizational framework for understanding the American state. It concludes with an overview of the book’s chapter structure, major themes, and narrative strategies.