The ankle-foot-orthosis (AFO), originally called Codivilla spring, is an orthotic device prescribed to the patients with foot drop due to neurological diseases in order to control the range of motion of the ankle joint and to compensate the muscle weakness/spasticity, thus optimizing the gait function. In this paper, a historical revision of the most known and used AFO worldwide from the origin of its name and the first applications at the Rizzoli Orthopedic Institute to the most advanced solutions in use today is covered. Through the critical analysis of the historical documents available, the paper reports on the controversy about the true inventor of the Codivilla spring during the first decades of the XX century. In terms of their design and indications, adult and child AFOs are presented. Finally, possible approaches for the selection of the correct orthosis and the individual prescription are discussed in order to manage specific mechanical neuromuscular deficiencies of the subject's ankle-foot complex, optimizing walking efficiency.