Trust is present from a very young age, but its expression in social interactions shows important changes over the lifetime. This chapter summarizes the research on age differences in trust, and explores the differences between males and females. Trust behavior can be measured using the trust game, which simulates a social interaction. Research shows that at a young age, trust is present at the start of the interaction but it is yet unclear whether this increases throughout development. Studies indicated an increase in the ability to adapt trust behavior, as well as an increase of reciprocity behavior throughout adolescence. Relatedly, an increase of activity in mentalizing-related areas and a decrease of activity in areas related to reward and conflict monitoring during adolescence and young adulthood is found. Often, males show more trust behavior than females although these differences are small. Sex differences in reciprocity behavior are found less often. Neuroimaging studies showed males have more activity in mentalizing-related areas while females show more activity in areas associated with reward and learning processes. Future studies may examine individual differences in the neural mechanisms of trust in relation with social context factors, such as cultural orientation or socioeconomic status.