Congressional Research Service. February 6, 2013. 

Special Operations Forces (SOF) play a significant role in U.S. military operations, and the Administration has given U.S. SOF greater responsibility for planning and conducting worldwide counterterrorism operations. U.S. Special Operations Command (USSOCOM) has about 63,000 active duty, National Guard, and reserve personnel from all four services and Department of Defense (DOD) civilians assigned to its headquarters, its four components, and one sub-unified command. The 2010 Quadrennial Defense Review (QDR) directs increases in SOF force structure, particularly in terms of increasing enabling units and rotary and fixed-wing SOF aviation assets and units. 

http://fpc.state.gov/documents/organization/204123.pdf [PDF format, 19 pages].