Start-ups and other entrepreneurial ventures make a significant contribution to the US economy, particularly in the tech sector, where they comprise some of the largest and most influential companies. Yet for every start-up that becomes a high-profile, high-growth company like Apple, Facebook, Microsoft, and Google, many more fail. This enormous heterogeneity poses conceptual and measurement challenges for economists concerned with understanding how new businesses affect economic growth. This volume brings together economists and data analysts to discuss the most recent research covering three broad themes. The first chapters isolate high- and low-performing entrepreneurial ventures and analyze their roles in creating jobs and driving innovation and productivity. The next chapters turn the focus on specific challenges entrepreneurs face and how they have varied over time, including over business cycles. The final chapters explore core measurement issues, with a focus on new data projects under development that may improve our understanding of this dynamic part of the economy.