Taking advantage of the rapid expansion of the Internet and the development of social media, extremist organizations have made cyberspace a hub for their radicalization and recruitment activities in recent years. Online propaganda distributed by terrorist organizations, such as ISIL and al-Qaeda, have led to the radicalization of individuals, inspiring them to become foreign fighters, engage in terrorist activity at the behest of organizational leadership, or carry out lone-wolf attacks. Through the use of different tactics, governments, civil society organizations, international institutions, and even private companies are currently exploring ways in which to counter online extremist propaganda and contain terrorist organizations’ cyber footprints. Radicalization represents a gateway issue for stakeholders trying to grasp a firm understanding of extremist groups’ multifaceted online activity and cyber potential. Forming a coherent strategy at the national and, subsequently, international level to address propaganda dispersion and the threat of radicalization is vital for governments in this regard. This assessment lays out the threat posed by radicalization via online extremist content, references the types of materials present on the Internet and the different platforms on which this content appears, explores a sampling of the various tactics used to suppress or engage online extremism, examines some of the impediments and achievements made at the international level regarding terrorism and the Internet, and ultimately offers suggestions for states in their development of comprehensive strategies for countering online radicalization, with the aim of subsequently sharing lessons learned with countries still developing their cyber capabilities and international institutions.