USA Track & Field
USATF Mountain, Ultra, Trail Council
All American Trail Running Association
Road Runners Clubs of America
Running USA
USATF Road Running Information Center
Ultrarunners Supporting Ultrarunners (USU)
 
 

International Organizations

International Association of Ultrarunners (IAU)
International Amateur Athletic Federation
Ass'n of International Marathons & Road Races
Athletics Canada
Atlas Athletic Association (Russia)
Association of Canadian Ultrarunners (ACU)
Association of Road Racing Statisticians
Australian Utrarunners' Association
British Athletics
German Ultramarathon Association
Ultra Netherlands (in Dutch)

Arkansas Ultrarunning Association (AR)
Badgerland Striders (WI)
Bay Area Ultrarunners (CA)
Broadway Ultra Society (NY)
The Incline Club (CO)
Kansas Ultrarunners' Society (KS)
New York Ultrarunning (NYC Area)
North Texas Trail Runners (TX)
San Diego Ultra Running Friends (CA)
Sri Chinmoy Marathon Team (NY)
St. Louis Ultrarunning Group (MO)
Trail Animal Running Club (MA)
Virginia Happy Trails Running Club (VA)
 
 

International Clubs

Ontario Ultra Series (CAN)
Sydney Striders (AUS)

Marathon & Beyond
Podismo (Italian)
Trail Runner
Ultrarunning Magazine
 

Resources

UltraRunR Resource
Ultrarunner.net
Run100s.com (Stan Jensen)
The Ultramarathon Store