People navigate the social world by considering the invisible, but ever-present mental lives of themselves and others. I present three papers that push the boundary of what we know about mental state reasoning by testing children’s and adults’ knowledge of complex aspects of the mind. In Chapter 1, I tested whether children and adults incorporate temporal markers into their mental state reasoning. Eight- to 10-year-olds and adults estimated the time duration of emotions (e.g., feeling sad), desires (e.g., wanting strawberries), and preferences (e.g., liking strawberries). I found that children and adults hold lay theories about the time course of mental states: They viewed preferences as longer lasting than emotions and desires, expressed confidence in their duration judgments, and provided internally consistent responses that were reliable across a 1-week delay. In Chapter 2, I addressed adults’ beliefs about emotional responses to events as they unfold over time. LGBTQ-Latinx, LGBTQ-White, Straight-Latinx, and Straight-White participants integrated the valence (positive versus negative) and timing of events (first versus last in a sequence) into their emotion ratings. Across demographic groups, adults expected past negative events to shape reactions to later positive events, but prior positive events to have little influence over responses to subsequent negative events. Finally, in Chapter 3, I measured children’s and adults’ inferences about the abilities, preferences, and traits of a novel social group. I discovered that participants used their knowledge of one group to make inferences about an unknown group in the form of a dichotomizing heuristic—what is true of one group must not be true of another group. Adults widely applied this cognitive shortcut when inferring benign (e.g., liking apples), novel (e.g., playing daxes), and even evaluative group characteristics (e.g., being smart). The common thread connecting these papers is an aim to move beyond thinking about mental states as isolated experiences to integrate the broader contexts in which they occur.