Trust is the currency on which all human interactions are based. This entry reviews a diverse body of literature on the development of trust. We begin by describing foundational theories linking early experience to trust, and then discuss how violations of trust affect children. We turn next to a particularly active area of trust research in cognitive development—namely, trust in information learned from what other people say (testimony). Children's willingness to believe what they are told is essential for the cultural transmission of knowledge; it allows them to learn about things they have not experienced themselves. We describe research showing that, in fact, young children have a great deal of difficulty not believing testimony. We suggest that this credulity is the manifestation of a bias to trust testimony specifically rather than a more generic, undifferentiated trust, and speculate about the origins of this bias. Finally, we offer several suggestions of areas for future research, including whether children (like adults) make judgments of trustworthiness based on an individual's facial features, how culture influences trust and trustworthiness, and how children learn to evaluate the credibility of digital sources of information.