Radicalization is the process by which an individual moves from mainstream political, religious, or social beliefs to a more extreme and intolerant belief system. Although radicalization does not always lead to violence, the process is a necessary precursor to acts of violent extremism and terrorism. Radicalization depends on a multitude of factors that are often times interconnected, including internal motivations and external pressures or catalysts.

Although radicalization has traditionally taken place through group-level association, technological advances have enabled elements of the radicalization process to move online. Cases of U.S. domestic terrorists, foreign fighters, and terrorist financiers reveal that an interest in extremism can be sparked or nurtured by viewing extremist content online. U.S. court documents, for example, frequently reveal the influence of lectures by extremist cleric Anwar al-Awlaki on the radicalization process of U.S.-based extremists.