In the past 20 years, the U.S. government, championed by the U.S. Department of Homeland Security (DHS) and in collaboration with other public and private entities, has made considerable progress enumerating the country's critical infrastructure components and National Critical Functions (NCFs). However, these efforts have not enabled specific identification of the most-critical computing systems within networks. To help fill that gap, researchers from the Homeland Security Operational Analysis Center sought to examine and enumerate the businesses that provide the most-critical information technology (IT) products and services and lay the groundwork for DHS and other federal and private-sector elements to better apply a risk-based approach to protecting the country's most-important assets and systems. They sought to (1) create a prioritized list of software and businesses that provide IT products and services and (2) develop a framework that could continue and extend this analysis into the future to accommodate emerging technologies and the evolution of the technology market. The work featured four workstreams: (1) identifying and integrating disparate data sources to identify the most-critical vulnerabilities and software applications in the U.S. internet protocol space; (2) collecting original data to map the software dependency and ownership structure of the most-referenced libraries; (3) leveraging existing work to identify specific IT and communication companies that were most interconnected and could suffer the greatest economic loss; and (4) developing a way to link NCFs to actual software companies supporting those functions.