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 where improvement to digital infrastructure benefits both sets of users. Despite its importance for economic performance, frontier 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. It stresses the large number of unanswered policy-relevant research questions where economic analysis could inform discussion.