Nonprofit equine rescue organizations in the United States provide care for relinquished horses and may offer adoption programs. With an estimated 100,000 "unwanted" horses per year and few municipal shelters providing wholesale euthanasia, there is a need to minimize the number of unwanted horses and maximize their successful transition to new caregivers. This study's objectives were to characterize the relinquishing and adoptive owners interacting with nonprofit rescue organizations. Nonprofit organizations (n = 144) in 37 states provided information by survey on 280 horses relinquished between 2006 and 2009, from which 73 were adopted. Results show the majority of relinquishing owners were women, whereas adoptive owners were primarily families or couples. Most relinquishing owners had previous equine experience and had owned the horse for 1 to 5 years; about half owned 1 other horse. Three quarters of the adoptive owners possessed additional horses housed on their property. The primary use for rehomed horses was for riding or driving. These findings will serve to help develop effective education programs for responsible horse ownership and optimize acceptance criteria and successful adoption strategies of horses by nonprofit organizations.