Providing safe, secure and reliable digital communication is a critical global issue. While the Internet is the most noticeable public mechanism, financial institutions, defense contractors, and many other enterprises rely on internal networks to securely transmit data. Configuring networks is an error-prone task, and small mistakes can lead to big outages or vulnerabilities. Public examples of this include last year's Amazon Web Services outages, which brought down sites like Reddit and Airbnb and left Netflix subscribers unable to stream video. As part of his Ph.D. research at Princeton, Cole Schlesinger designs tools and programming languages to make building networks safer and easier. His work draws on formal programming languages theory, including operational semantics, algebra, and logic, to provide strong peoperties about the resulting systems. Cole has developed new techniques for safely updating enterprise and datacenter networks and new theories for reasoning about how collections of network devices behave. Cole's work on network programming languages is the most recent of several projects focused on applying formal methods to improving the security and reliability of real systems.