Gonioscopy is the gold standard for diagnosis and evaluation of all forms of glaucoma. It allows the examiner to actually see any obstruction to the aqueous drainage in the anterior chamber angle by direct visualization of the trabecular meshwork and its adjacent structures. A number of congenital and acquired diseases affecting the eye can be picked up by performing a detailed gonioscopic evaluation and the primary diagnostic use of gonioscopy is to distinguish open angle versus closed angle mechanisms for glaucoma. Other critical uses of gonioscopy are picking up neovascularization of the angle in eyes with posterior segment ischemia, detection of abnormal pigmentation and anomalies associated with closed globe injuries. In addition to the diagnostic utility of gonioscopy, with recent advances in glaucoma surgery, a number of microsurgical techniques now require intraoperative gonioscopy to be used for inserting glaucoma implants into the Schlemm’s canal or supraciliary space. The current text and atlas on gonioscopy is a comprehensive compilation of our experience and documentation of glaucoma patients over the last two decades. It includes the principle, indications and types of gonioscopy, the techniques for dynamic gonioscopy, classification systems, evaluation of normal anterior chamber angles and clinical findings in various forms of congenital and acquired glaucomas. Additionally, conditions such as ocular tumors, foreign bodies, post-surgical complications, systemic disorders with angle anomalies, etc. have been incorporated. There is a special section on RetCam gonioscopy, intraoperative gonioscopy and gonioscopy after glaucoma surgery including minimally invasive glaucoma surgery. The atlas has over 600 photographs and gives the readers a clear visual understanding of the disease process. This text and atlas will help in imparting the trainees an in-depth knowledge of gonioscopy, and would help in the correct diagnosis and treatment of glaucoma.