Fibrodysplasia ossificans progressiva (FOP), a rare and disabling genetic condition characterized by congenital malformations of the great toes and progressive heterotopic endochondral ossification (HEO) which is the most catastrophic of HEO disorders in humans. Flare-ups of FOP are episodic; immobility is cumulative. Heterozygous activating mutations in activin receptor IA/activin-like kinase-2 (ACVRI/ ALK2), a bone morphogenetic protein (BMP) type I receptor, exist in all sporadic and familial cases of FOP. The discovery of the FOP gene established a critical milestone in our understanding of FOP, and revealed a highly conserved therapeutic target in the BMP signaling pathway. This discovery has advanced efforts to develop novel therapies for this disabling disorder of tissue metamorphosis. While effective treatment of FOP will likely be based on interventions that modulate overactive ACVR1/ALK2 signaling, or that specifically block postnatal HEO, current management is focused on early diagnosis, assiduous avoidance of injury or iatrogenic harm, symptomatic amelioration of painful flare-ups, and optimization of residual function.