Compassion appeals are employed to mobilize prosocial actions that address global grand challenges. However, the evidence of the effectiveness of such appeals is still mixed, with studies using a multitude of persuasion appeals and examining diverse outcomes. To explain the mixed findings, we conduct an integrative, critical review of 77 articles (altogether reporting 116 empirical studies) on the role of compassion appeals in motivating prosocial behavior. This review explains the conditions that determine the relative effectiveness of compassion appeals. First, we identify the appeal components and contextual factors that elicit compassion. Successful elicitation is a prerequisite for the effectiveness of compassion appeals. Second, we reveal that compassion often is elicited with distress, an emotion actively regulated by audiences. Consequently, persuasive compassion appeals are most effective when elicited compassion is maintained within an area of acceptability, demarcated by elicitation and backfiring thresholds. Third, we show that mixed findings are often due to a mismatch between the motivation elicited by compassion and the prosocial action encouraged by the appeal. Compassion motivates the relief of immediate suffering but is not suited to drive sustained commitment toward promoting structural social change. To address this limitation of compassion, we conceptualize the need for compassion blends, mixed emotions where compassion is elicited along with guilt and/or moral anger. We explain why and how compassion blends can motivate transformative prosocial behavior. The results from our critical review inform an agenda for future research and offer actionable insights for the design of effective compassion appeals.