Passion energizes and directs both peaceful and violent ideologically inspired movements. The type of ideological passion that underlies people's political or religious commitment was proposed to moderate the effect of social identity–threatening circumstances on their choice of activist tactics. Ideological passion was defined as a strong inclination toward a loved, valued, and self-defining cause, ideology, or group in which people invest considerable time and energy. Harmonious ideological passion was expected to promote peaceful activism and nonviolence partly because it is anchored in a strong and secure sense of identity—one that facilitates nondefensiveness in identity-threatening circumstances. Obsessive ideological passion, in contrast, was expected to engender hatred and aggressive extremism in identity-threatening circumstances partly because it is anchored in a strong, but insecure, sense of identity. Results from 2 studies, conducted with nationalist activists (N = 114) and devout Muslims (N = 111), supported these hypotheses. Implications for the motivation/passion and intergroup literatures are discussed.