This book explains why, when, and how to treat eye motility disorders. It starts with a discussion of the general principles of eye motility and its importance in creating binocular single vision with depth perception. It also reviews the most important parts and functions of the sensory and motor eye motility system for those new to the field of ophthalmology. The book also describes different types of strabismus and the treatment for each type. Special care is taken to explain the difference between causes, diagnostics, and treatment of eye motility disorders in children with immature visual system and, on the other side, in adult cases when development is already finished. It describes the steps of orthoptic assessment, with a special interest in tests for binocularity. It also presents different conservative treatment possibilities, including glasses, prisms, orthoptic exercise, Botox, and so on. In cases where conservative treatment is not enough, surgery is the method of choice. The choice of surgical treatment depends on the age of the patient, the type of strabismus, and the muscle involved. The book thus presents the principles of surgeries along with explanations and figures.