OSSA is an indigenous humanitarian organization working in communities to reduce the spread of HIV/AIDS in Ethiopia. OSSA was founded in 1989 by a group of religious ministers from the various faiths in Ethiopia (Orthodox Christian, Catholic, Muslim and Evangelical) in conjunction with the Ministry of Health. The founding of OSSA was a response to the growing incidence of HIV/AIDS in Ethiopia.
OSSA now operates through nine main branches in major towns and cities where the prevalence of HIV/AIDS is highest. The Mekelle main branch was established in October 1994, with a paid coordinator and a number of voluntary staff. The voluntary staff became paid staff in 2003, after 7 years of voluntary service, and the office how has 10 full-time professional staff.