Gus Martin's Understanding Homeland Security provides students with a comprehensive introduction to U.S. homeland security in the modern world, with a focus on the post-September 11, 2001 era. This insightful resource examines the theories, agency missions, laws, and regulations governing the homeland security enterprise through the lens of threat scenarios and countermeasures related to terrorism, natural disasters, emergency management, cyber security, and much more. The Third Edition keeps readers on the forefront of homeland security with coverage of cutting-edge topics, such as the role of FEMA and preparedness planning; the role of civil liberty and countering extremism through reform; and hackings during the 2016 and 2018 U.S. elections. Readers will gain much-needed insight into the complex nature of issues surrounding today's homeland security and learn to think critically to analyze and respond to various threat environments.