This chapter provides a theory of the ethics of revolution and the ethics of interventions in revolutions. It sets the stage for the ethical discussion by using the descriptive-explanatory theory of revolution laid out in Chapter 3 to identify the special ethical problems revolutionaries face and the consequences for intervention of the ways in which revolutionaries will typically address those problems. The chapter states and criticizes two widely accepted principles that are supposed to provide guidance to potential interveners in revolutions. The first is the principle that no intervention should be undertaken without the consent of the people in the country that is the target of the intervention. The second is the principle, advocated by John Stuart Mill, that widespread participation in a movement to overthrow the existing regime, understood as an indication of a pervading commitment to revolution, is a necessary condition for justified intervention. This chapter argues that neither principle provides useful guidance as to intervention because both ignore certain features of real-world revolutions. This conclusion confirms an important thesis of the book, namely, that normative inquiries about social change, including investigations to articulate the ethics of revolution and intervention in revolution, must be grounded in an accurate understanding of the morally relevant facts about the phenomena in question. This chapter also extends and deepens the discussions of the explanatory power of the concept of ideology first developed in Chapters 2 and 3, arguing that ideologies can serve to rationalize the use of coercion and violence that otherwise would be regarded as morally prohibited. Finally, this chapter explains how the choice is not between morality and self-interest as drives of social change but is rather a matter of understanding how self-interest can be served by the strategic employment of moral concepts and principles.