Strabismus is one of the earliest documented ophthalmic conditions. In ancient times, it was considered incurable, secondary to inhabitation by an evil spirt.1 Early Greco-Roman treatments included potions, dietary modifications, and masks to force redirection of the visual axes.1 In the 10th/11th century, a period during which Muslims were at the forefront of ophthalmology, ‘Ali bin ‘Isa of Baghdad advocated treatment of strabismus by straightening the eyes.1 The use of refractive correction and extraocular muscle surgical procedures evolved in Europe from the 17th to 19th century. The concept of fusion training and the profession of orthoptics developed in Europe and America during the 19th and early 20th centuries. For much of the 20th century, basic strabismus assessment and management remained relatively unchanged. However, from the end of the 20th century to currently in the 21st century there have been significant conceptual and surgical advances, particularly for incomitant strabismus. In this special issue of Middle East African Journal of Ophthalmology, experts in the field highlight modern concepts in the assessment and management of incomitant strabismus.Surgery is often indicated for incomitant strabismus. Like all forms of surgery, strabismus surgery carries a risk of error and/or complication, which can occur during diagnostic assessment and/or be related the actual surgery itself. It is important to understand the most common sources of errors/complications in order to minimize them. Irsch2 provides an overview of clinically-relevant optical issues in strabismus assessment, with emphasis on sources of angle measurement error. Olitsky and Coats3 review the most common and/or devastating complications associated with strabismus surgery and how to minimize them.Recognition of the complexity of extraocular muscle orbital anatomy is perhaps the most significant modern scientific advancement in strabismus because of its translational clinical relevance. Clark4 reviews key biomechanical concepts of the extraocular muscle pulleys, pulley disorders as a cause of incomitant strabismus, and strabismus surgical techniques that specifically address pulley disorders. Leuder5 shares his experience with common orbital factors other than extraocular muscle pulley disorders that can underlie incomitant strabismus. Stager and colleagues6 review the unique anatomy of the inferior oblique muscle and its neurovascular bundle and how different inferior oblique procedures can take advantage of this unique anatomy.Children who present to ophthalmologists with strabismus typically have ocular disease only. Those with strabismus related to refractive error are often hyperopic or anisohyperopic, but some children and adults present with strabismus in the context of myopia. Ramesh and colleagues7 highlight issues that are unique to myopic strabismic patients. A small subset of strabismic children who present to ophthalmologists actually have an undiagnosed brain tumor rather than the isolated ocular disease. Alswaina and colleagues8 review the experience of the King Khaled Eye Specialist Hospital with children who first presented to ophthalmologists and based on ophthalmic examination were newly diagnosed with brain tumors. Most of the 26 children in the series had disk swelling or pallor in the context of decreased vision or strabismus, but 2/26 had apparently isolated unilateral sixth nerve palsy. Although a classical teaching for apparently isolated sixth nerve palsies in children was to follow without imaging unless the palsy failed to resolved or further neurological signs developed, it seems more prudent in the modern era of high resolution neuroimaging and precision neurosurgery that all such cases undergo early neuroimaging.Acquired incomitant strabismus with diplopia in adults is the most challenging form of strabismus to manage, especially when more than one extraocular muscle is involved. Al Qahtani and colleagues9 share clinical pearls and management recommendations regarding thyroid orbitopathy-related strabismus, for which restrictive and secondary innervational factors are important to recognize. Murray10 provides an approach for assessing patients with incomitant strabismus after ocular or orbital trauma and reviews surgical techniques for retrieving or compensating for damaged or “lost” extraocular muscles. Saxena and colleagues11 discuss indications and techniques for fixation of the globe and/or extraocular muscle to the orbital wall, an approach that is indicated for certain forms of acquired traumatic or dysinnervational strabismus as well as certain forms of congenital dysinnervational strabismus.