Anxiety & Depression Association of America: http://www.adaa.org/understanding-anxiety/obsessive-compulsive-disorder-ocd
Beyond OCD: http://beyondocd.org/ocd-facts
Mayo Clinic: http://www.mayoclinic.org/diseases-conditions/ocd/basics/definition/con-20027827
National Alliance on Mental Illness: http://www.nami.org/Template.cfm?Section=By_Illness&Template=/TaggedPage/TaggedPageDisplay.cfm&TPLID=54&ContentID=23035
National Institute Of Mental Health: http://www.nimh.nih.gov/health/topics/obsessive-compulsive-disorder-ocd/index.shtml
OCD Foundation: http://www.ocfoundation.org/whatisocd.aspx