Otosclerosis (localized bone dysplasia) is a primary disease of the human otic (labyrinthine) capsule and stapes footplate. Depending on the site, size, and histologic features of the pathologic involved area hearing and balance are affected. When describing otosclerosis, it is important to distinguish between the histological and the clinical form of the disease. Clinical/radiological otosclerosis refers to the presence of otosclerotic foci at the site where it causes conductive hearing loss by interfering with the motion of the stapes or of the round window membrane. The main therapeutical choice is stapes surgery. However, rarely alternative surgical approaches may be required such as bone anchored implantable devices, middle ear implants or cochlear implants, based on patient conditions and the severity of hearing loss. The patient should have a PTA demonstrating a conductive or mixed hearing loss (sometimes with a Carhart’s notch) with a large enough ABG and absent stapedial reflexes. The affected ear should be the worse hearing ear. Speech discrimination should be sufficient to justify the risk of the procedure. Clinical examination should exclude other middle ear disease and the tympanic membrane should be intact. Imaging can help to confirm the clinical diagnosis or exclude other pathologies.