Equine-assisted therapy for posttraumatic stress disorder (EAT-PTSD) treatment protocol was developed by the Man O’ War Project (MOW Project) at Columbia University Irving Medical Center. Led by Prudence Fisher and Yuval Neria, the MOW Project began in 2015 with the goal to establish the efficacy and effectiveness of EAT for military veterans who have PTSD. An iterative process, with input from a wide range of “experts” and pilot testing, was used to produce a protocol that could be tested (EAT-PTSD), which was then manualized and tested in a large open trial (n = 63) with positive results: significant improvement in PTSD and depressive symptoms, no safety concerns, with only five participants not completing treatment. EAT-PTSD is an eight-session, group treatment designed to address important clinical issues typical of individuals with PTSD. Groups comprising four to six veterans are facilitated by a treatment team (licensed mental health professional and equine specialist, each with a defined role) with two or three horses. Engaging in progressively complex ground activities (there is no riding) with horses helps participants develop greater awareness of internal emotional cues, become more attuned to others, communicate more effectively, and increase self-confidence. Teamwork and interactions with other group member also bolster feelings of self-efficacy and safe connection with others. While controlled studies are needed to establish efficacy, EAT-PTSD shows promise as an effective primary intervention or adjunctive therapy for PTSD or PTSD symptoms. The comprehensive EAT-PTSD treatment manual and the EAT-PTSD training curriculum allow for implementing the protocol by practitioners from different sites or programs.