The current study utilized longitudinal data to investigate how theory of mind (ToM) and emotion understanding (EU) concurrently and prospectively predicted young children's moral reasoning and decision making. One hundred twenty-eight children were assessed on measures of ToM and EU at 3.5 and 5.5 years of age. At 5.5 years, children were also assessed on the quality of moral reasoning and decision making they used to negotiate prosocial moral dilemmas, in which the needs of a story protagonist conflict with the needs of another story character. More sophisticated EU predicted greater use of physical- and material-needs reasoning, and a more advanced ToM predicted greater use of psychological-needs reasoning. Most intriguing, ToM and EU jointly predicted greater use of higher-level acceptance-authority reasoning, which is likely a product of children's increasing appreciation for the knowledge held by trusted adults and children's desire to behave in accordance with social expectations.