Long-Lived Particles and the Future of Particle Physics

<!--HTML--><p>​The gold standard for progress in particle physics is the discovery of new elementary particles. For decades the search for new particles focused on heavy particles with short lifetimes. More recently, however, there has been a paradigm shift, with a new focus on long-lived particles that can be either heavy or light. Such particles appear in many theories designed to address the outstanding questions of neutrino mass and dark matter, and the possibility that they exist has led to an explosion of new ideas for particle searches through a wide variety of experiments. This talk will place the paradigm shift toward long-lived particles in its historical context, highlight some of the ongoing experiments that are already yielding interesting results, and provide an outlook for the future.</p>