The al-Qaeda Organization (AQO) and the Islamic State Organization (ISO) are transnational adversaries that conduct terrorism in the name of Sunni Islam. It is declared U.S. Government (USG) policy to degrade, defeat, and destroy them. The present book has been written to assist policymakers, military planners, strategists, and professional military educators whose mission demands a deep understanding of strategically-relevant differences between these two transnational terrorist entities. In it, one shall find a careful comparative analysis across three key strategically relevant dimensions: essential doctrine, beliefs, and worldview; strategic concept, including terrorist modus operandi; and specific implications and recommendations for current USG policy and strategy. Key questions that are addressed include: How is each terrorist entity related historically and doctrinally to the broader phenomenon of transnational Sunni "jihadism"? What is the exact nature of the ISO? How, if at all, does ISO differ in strategically relevant ways from AQO? What doctrinal differences essentially define these entities? How does each understand and operationalize strategy? What critical requirements and vulnerabilities characterize each entity? Finally, what implications, recommendations, and proposals are advanced that are of particular interest to USG strategists and professional military educators?