Obesity is defined as a body mass index (BMI) ≥ 30 kg/m2. In some Asian countries (e.g., China and Japan), the BMI threshold to define obesity is lower. Obesity is a major health problem worldwide inflicting high cost to the society. The prevalence of obesity has doubled in more than 70 countries since 1980. The number of adult subjects with obesity is around 650 million worldwide. The COVID-19 pandemic may significantly increase this number. Obesity can be associated with comorbidities including hypertension, dyslipidemia, type 2 diabetes, atrial fibrillation, ischemic heart disease, sleep apnea, nonalcoholic fatty liver disease, osteoarthritis, cancer, and depression. In the management of obesity, any medical condition contributing to weight gain should be treated. In addition to preventive measures, management of obesity requires multidisciplinary approaches including lifestyle (e.g., diet, exercise, and behavioral change), food supplements, drugs (e.g., Phentermine, Orlistat, Phentermine + Topiramate, Naltrexone + Bupropion, Liraglutide, and Semaglutide), medical devices (e.g., gastric band, intragastric balloon, and superabsorbent hydrogel), gut microbiome modulation (e.g., prebiotics and probiotics), body contouring (e.g., liposuction), and bariatric surgery (e.g., sleeve gastrectomy and Roux-en-Y gastric bypass). There are gender differences in the outcome of several weight-loss treatment. For a similar weight loss, men usually lose more visceral fat and less subcutaneous fat compared to women. Even a modest weight loss can decrease the risk of several comorbidities of obesity. In the USA, only a small percentage of subjects with obesity (around 2%) who are eligible for antiobesity drugs and less than 1% of subjects with obesity who are eligible for bariatric surgery benefit from these treatments. The reasons for these undertreatment rates are mainly related to adverse effects and cost of anti-obesity drugs and bariatric surgery. Long-term weight maintenance remains a challenging goal for most patients and physicians.