This chapter provides a comprehensive overview of type 1 diabetes (T1D), focusing on its pathophysiology, clinical stages, management, and complications. T1D arises from an autoimmune response affecting insulin-producing beta cells, with contributions from genetic, epigenetic, environmental, and islet-related factors. Key genetic risk factors, primarily related to specific HLA genes, are highlighted alongside newly identified risk loci through advanced methods such as genome-wide association studies. The preclinical stages of T1D are categorized into three defined stages, emphasizing the importance of early detection and monitoring of islet autoantibodies to reduce the risk of diabetic ketoacidosis (DKA) and explore interventions for beta-cell preservation. Advances in technology, particularly continuous glucose monitoring (CGM) systems and automated insulin delivery (AID), have revolutionized blood glucose regulation and reduced complications such as hypoglycemia. School-based management is discussed to ensure safety and support during academic and social development for children with T1D. Acute complications like DKA and hyperosmolar hyperglycemic state (HHS), along with chronic complications ranging from microvascular to macrovascular disease, are covered in detail to highlight the importance of diligent long-term care. Emerging therapies like teplizumab underscore the potential for delaying or preventing progression to insulin dependence. The chapter concludes by emphasizing the importance of individualized care and continued research into genetic and environmental factors driving T1D heterogeneity.