This book aims to provide information on basic principles of squint and orthoptics to the residents in ophthalmology and students of orthoptics and optometry. The book would be equally useful for the practising ophthalmologists, optometrists and orthopticians as well. To keep it a basic book, advanced theories and many diverse opinions have been excluded. The text has been organized into fifteen chapters. First four chapters have been devoted to the anatomical and physiological aspects of extra ocular muscles, vision, and binocular vision. The remaining eleven chapters have been planned to provide a clear insight of the various disorders of ocular motility.