In this concise JSOU monograph, Dr. Rich Yarger considers the 21st century security environment, previous work on special operations theory, and various other perspectives of SOF gleaned from his research to synthesize an American SOF school of thought, which he argues provides a foundation for developing an American special operations theory for the 21st century. He offers definitions, premises, and principles that explain modern American special operations over the last 70 years and can serve SOF well into the future. Based on his research, he identifies major areas of concern for SOF leadership. As USSOCOM confronts the challenges offered by the 21st century and policymakers continue to look at SOF as a preferred means to address numerous and complex security issues, theory is essential in determining and explaining the appropriate roles and missions for SOF in the 21st century.