In 2001, Rutledge reported the first case of mini gastric bypass (MGB). Carbajo improved the technique of MGB and named it one anastomosis gastric bypass (OAGB). Over the past 20 years, a large number of clinical and basic studies on OAGB/MGB have been reported, and the answers to some key questions about OAGB/MGB have gradually become clear. From a technical point of view, MGB and OAGB can be regarded as two subvariants of one surgery. The advantages of OAGB/MGB include: (1) simplicity, safety and lower probability of internal hernia;(2) stable and durable weight reduction effect; (3) stable and durable remission rate of type 2 Diabetes. The disadvantages of OAGB/MGB include: (1) bile reflux; (2) higher risk of malnutrition. OAGB/MGB has achieved a good balance between effectiveness and safety, and has become the most noticed and fastest-growing bariatric and metabolic procedure in recent years. OAGB/MGB has been recommended as a standard bariatric and metabolic procedure by IFSO and ASMBS.