Hyperglycemia, defined as elevated blood glucose levels, is a hallmark feature of diabetes and a key contributor to both acute and chronic complications. Acute hyperglycemia can result in life-threatening conditions such as diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS), particularly in poorly controlled diabetes. Chronic hyperglycemia leads to microvascular complications—retinopathy, nephropathy, and neuropathy—and contributes to macrovascular diseases including coronary artery disease and stroke. The underlying causes of hyperglycemia vary by diabetes type: insulin deficiency in Type 1 diabetes and insulin resistance coupled with β-cell dysfunction in Type 2 diabetes. Stress, illness, medications (e.g., corticosteroids), and inadequate diabetes management can all exacerbate hyperglycemia. Monitoring tools such as self-monitoring of blood glucose (SMBG), continuous glucose monitoring (CGM), and HbA1c testing are essential for detection and control. Effective management includes tailored pharmacologic therapy, lifestyle modification, and education on carbohydrate intake and insulin dosing. Timely intervention to address hyperglycemia is crucial to prevent long-term damage and improve outcomes in patients with diabetes.