The Tor anonymous communication system helps millions of users every day to use the Internet more safely, protecting their identity, blocking tracking, and in some cases circumventing censorship. Since its creation in 2005, the Tor Project has worked to enhance the usability and security of Tor, bringing it from a research prototype with a handful of users to an easy-to-use modern application today. In this talk, I’ll discuss the research challenges that had to be addressed during this journey and open research questions that remain, including on usability, traffic-analysis resistance, ethical considerations, and post-quantum cryptography.