This session will cover the classification of diabetes mellitus, including type 1, type 2, gestational, and secondary diabetes, along with their underlying pathophysiology. The discussion will focus on insulin deficiency, insulin resistance, and the role of autoimmunity and metabolic dysfunction. Clinical implications include early recognition of symptoms, risk factors for complications such as neuropathy, nephropathy, and cardiovascular disease, and the importance of timely intervention to prevent long-term morbidity.