The prevalence of obesity has become an epidemic among westernized societies and a leading cause of non-communicable disease associated with numerous comorbidities, including diabetes, chronic inflammatory disease, and cancers. In the most morbidly obese patients, bariatric and metabolic surgical interventions are the most effective interventions for weight loss and are associated with rapid improvements in metabolic health. Contributing factors to the efficacy of metabolic surgery include changes in gut signaling pathways – including the enteric nervous system and enteroendocrine hormones – altered food preference, delayed absorption, enhanced thermogenesis, altered enterohepatic circulation, and reshaping of the gut microbiota communities. This chapter will focus on the rise of metabolic surgery for the treatment of obesity and related comorbidities, followed by the state of knowledge regarding mechanisms of action. Bariatric interventions alter the gut microbiome and its interaction with host metabolites, including bile acid pools. We review the interactions between the host, the gut microbiome, bile acid metabolites, and immune function underpinning improved metabolism in obesity, through central and peripheral mechanisms, following metabolic surgery.