Palovarotene (formerly RO-3300074; R-667) is a novel, potent and highly selective retinoic acid receptor gamma (RAR-γ) agonist that is being investigated as a potential treatment for emphysema. Palovarotene effectively inhibited HO in injury-induced and genetic mouse models of the disease. It additionally prevents spontaneous HO, using a novel conditional-on knock-in mouse line carrying the human ACVR1(R206H) mutation for classic FOP. In addition, palovarotene restored long bone growth, maintained growth plate function, and protected growing mutant neonates when given to lactating mothers. Importantly, palovarotene maintained joint, limb, and body motion, providing clear evidence for its encompassing therapeutic potential as a treatment for FOP.