Recently, the world has experienced a wave of violent protest, and in particular Islamist and right-wing extremism have become increasing challenges for many societies. We argue that especially the experience of relative deprivation, that is the perception that oneself or one’s group is undeservingly worse off than others, can explain various, contemporary forms of violent extremism, including (a) low-power groups’ violent attempts to challenge the unequal status quo, (b) high-power groups’ violent defense of their privileged position, and sometimes even (c) people’s violent attempt to help out-groups in need. In light of recent research and growing social inequalities, we expect relative deprivation to be a key factor driving violent extremism across cultures and contexts in the 21st century.