One of the major challenges in materials science today is developing materials that can survive and function in extreme environments, such as the high-radiation environments found in a fission or fusion reactor or the ultra-high temperature experienced by a hypervelocity vessel or a spacecraft traveling through Earth's atmosphere on its return to the planet's surface. What is needed to discover such materials was the topic of a 2-day workshop held at the National Academies of Sciences, Engineering, and Medicine on October 5-6, 2022. That workshop, titled Materials in Extreme Environments: New Monitoring Tools and Data-Driven Approaches, brought together an international collection of experts on the testing and measurement of materials in extreme environments and on discovering and developing new materials. This Proceedings of a Workshop recaps the presentations and discussions that took place during the 2 days of the workshop.