During the last decade, the One Anastomosis Gastric Bypass (OAGB) received almost worldwide acceptance and popularity as bariatric and metabolic procedure. Its technique is appearing rather simple and straight forward. Albeit, as in other such procedures, to avoid disappointing short- and longterm complications, certain essential principles need to be respected. With this goal in mind, this Masterclass course will present step by step a current standardized technique of OAGB. In addition, possible technical variations will be presented as well. The focus will be both on the crucial keypoints and on the avoidance of typical and specific technical failures, complications, and pitfalls.