Book excerpt: Terrorism: Commentary on Security Documents is a series that provides primary source documents and expert commentary on various topics relating to the worldwide effort to combat terrorism, as well as efforts by the United States and other nations to protect their national security interests. Volume 148, Lone Wolf Terrorists, examines the phenomenon of the solitary domestic terrorist, analyzes the distinction between such terrorists and mass murderers who are not deemed to be terrorists, considers the motivations of violent extremists, and examines the dilemmas faced by law enforcement in preventing solitary political extremists with violent ideologies from translating their beliefs into actions. The volume is divided into three sections, providing an overview of the topic, an examination of strategies for prevention of such attacks, and a consideration of the Internet's role in contributing to radicalization. Documents included in this volume include a CRS report on domestic terrorism, a report examining violent radicalization from a criminal justice perspective, and a CRS report differentiating hate crimes from domestic terrorism, as well as other reports on the lone wolf terrorism phenomenon and strategies to prevent and/or counter it. The last document in the volume is a CRS report relating to the advocacy of terrorism on the Internet, especially including social media, and the ways in which law enforcement might be able to address the problem of dangerous online speech within the current U.S. legal structure.