Science relies on trust. It couldn’t possibly proceed unless scientists working in one area were able to trust the results of scientists working in other areas. Even the most accomplished scientists today rely on the results of many other scientists to conduct their research. For this reason, science as an institution has standards for trustworthiness, both with respect to individual scientists and with respect to scientific claims. In this video, we’ll talk about the related ideas of testimony as a source of knowledge and scientific expertise. We’ll discuss how to judge a scientist’s expertise and the institutional practices of science that ensure its reliability. This video is aligned with Chapter 7 of the book Recipes for Science: An Introduction to Scientific Methods and Reasoning, by Angela Potochnik, Matteo Colombo, and Cory Wright.