What determines the supply of innovative digital infrastructure and how does variance in supply shape the performance of digital services? The essay reviews research into the economic impact of deployment, innovation, and adoption of digital infrastructure. It distinguishes between household and business use of access, and describes how and where improvement to digital infrastructure benefits both suppliers and users. Despite its importance for economic performance, digital infrastructure operates at a distinctive and evolving boundary between public and private, which frames many research questions. The essay focuses on the experience in the United States and it covers the global experience when possible, stressing policy-relevant research questions. A large number of unanswered questions can benefit from economic analysis.