The topic of terrorism is at the forefront of the world's attention and poses challenging questions concerning the psychological processes of radicalization and de-radicalization. Among the most pressing questions are: Why are individuals willing to end their lives to harm others? Can we change the hearts and minds of those that have already engaged in terrorism? In this talk, I present evidence suggesting that both radicalization and de-radicalization are driven by the same motivational force: The Quest for Personal Significance ("to matter", "to be respected", "to be someone"). Empirical evidence collected worldwide, including samples from various terrorist organizations, indicates that awakening the significance quest enhances individuals' willingness to self-sacrifice in the name of a cause and support for terrorism. On the other hand, I will present data on the first attempt to assess the effectiveness of a de-radicalization program, involving thousands of detained terrorists, suggesting that the significance quest can be turned around and redirected in a constructive direction, paving the way to conciliation, conflict resolution, pro-social behaviors, and harmonious intergroup relations.