This study explores the psychological, computational, and neural foundations of indebtedness, a feeling induced by receiving a favor from another person. The authors develop and validate a conceptual model of indebtedness through three studies: a large-scale online questionnaire, an interpersonal game, and neuroimaging. The model posits that indebtedness consists of two distinct components: guilt and obligation. Guilt arises from perceived altruistic intentions, while obligation stems from inferred strategic intentions. These feelings motivate reciprocity behaviors. The study finds that participants' appraisals of the benefactor's intentions influence their feelings of guilt and obligation, which in turn affect their decisions to accept or reject help. Computational models based on Psychological Game Theory predict reciprocity and help-acceptance decisions, capturing the tradeoff between communal concern and obligation. Neuroimaging results show that communal concern is associated with activity in the insula, ventromedial prefrontal cortex (vmPFC), and dorsolateral prefrontal cortex (dlPFC), while obligation is linked to the temporal parietal junction (TPJ) and dlPFC. A neural utility model constructed from brain activity successfully predicts reciprocity behavior, demonstrating that neural signals reflect the tradeoff between communal concern and obligation.This study explores the psychological, computational, and neural foundations of indebtedness, a feeling induced by receiving a favor from another person. The authors develop and validate a conceptual model of indebtedness through three studies: a large-scale online questionnaire, an interpersonal game, and neuroimaging. The model posits that indebtedness consists of two distinct components: guilt and obligation. Guilt arises from perceived altruistic intentions, while obligation stems from inferred strategic intentions. These feelings motivate reciprocity behaviors. The study finds that participants' appraisals of the benefactor's intentions influence their feelings of guilt and obligation, which in turn affect their decisions to accept or reject help. Computational models based on Psychological Game Theory predict reciprocity and help-acceptance decisions, capturing the tradeoff between communal concern and obligation. Neuroimaging results show that communal concern is associated with activity in the insula, ventromedial prefrontal cortex (vmPFC), and dorsolateral prefrontal cortex (dlPFC), while obligation is linked to the temporal parietal junction (TPJ) and dlPFC. A neural utility model constructed from brain activity successfully predicts reciprocity behavior, demonstrating that neural signals reflect the tradeoff between communal concern and obligation.