This Element addresses questions of increasing urgency surrounding public trust in science: what it is, how to earn it, and what to do when trust needs repair. The concept of trust is rooted in human relationships, and as such, applies to societies around the world. Funk draws from her experiences as a public opinion researcher at the intersection of science and policy. She illustrates practical lessons for trust from global, cross-national surveys. She discusses ways to earn trust in both small and large communities as well as common missteps in such efforts. She emphasizes the importance of active engagement with publics to build trust, especially to demonstrate scientists' benevolent intent and caring for public interests. She draws lessons for trust from emergent developments in science and technology, focusing on the case of AI. Her analysis highlights the interdependence of trust in scientists with government, universities and other institutions.