Uncompromising wars, revolution, rights movements, and today’s global terrorism are in part driven by Devoted Actors who adhere to sacred or transcendent values that generate actions independently, or all out of proportion, from rationally expected outcomes, calculated costs and consequences, or likely risks and rewards. Field-based observation, surveys and experimental studies in real-world political conflicts show ways in which Devoted Actors, who are unconditionally committed to sacred causes, and whose personal identities are fused within a unique collective identity, willingly make costly sacrifices including fighting and dying, thus enabling low-power groups to endure and often prevail against materially much stronger foes. Explaining how devoted actors come to sacrifice for cause and comrade not only is a scientific goal, but also a practical imperative to prevent and resolve seemingly intractable intergroup disputes that can spiral out of control in a rapidly interconnecting world of collapsing and conflicting cultural traditions in search of salvation. Fieldwork and experiments in Europe, North Africa and on the frontlines in the battle with the Islamic State in Iraq help to make the case.