The continued success of bariatric surgery as a treatment option for obesity requires a clinical understanding of the nutritional implications of abnormal adiposity with or without complications, as well as disruption of normal gastrointestinal anatomy and function. The 2019 AACE-TOS-ASMBS-OMA-ASA bariatric surgery clinical practice guidelines provide comprehensive perioperative nutritional recommendations. Beyond the dietetic principles necessary to maintain adequate nutritional intake, the main areas of interest in this chapter are macronutrient/micronutrient deficiencies and consequent organ dysfunction which can lead to cardiometabolic-based chronic disease, anemia, osteoporosis, neuropathy, nephrolithiasis, and bothersome constitutional symptoms. Nutritional issues should be considered in three broad categories: preoperative, early postoperative, and late postoperative. Specific perioperative nutrition concerns include formal nutritional assessments, aggressive case finding, and navigating evidence-based checklists and management protocols; nutritional aspects of diabetes care and hypoglycemia/dumping syndromes; prevention and management of bone loss and vitamin D deficiency; and prompt detection and appropriate interventions for overly rapid weight loss or problematic weight recurrence. Guideline-directed, routine perioperative nutrition care must be an integral part of the comprehensive approach to patients undergoing bariatric surgery.