Children rely extensively on others' testimony to learn about the world. However, they are not uniformly credulous toward other people. From an early age, children's reliance on testimony is tempered by selective trust in particular informants. Three- and 4-year-olds monitor the accuracy or knowledge of informants, including those that are familiar. They prefer to seek and endorse information provided by someone who has proved accurate in the past rather than someone who has made mistakes or acknowledged ignorance. Future research is likely to pinpoint other heuristics that children use to filter incoming testimony and may reveal more generalized patterns of trust and mistrust among individual children.