This document provides information about insulin therapy. It defines insulin as a polypeptide hormone secreted by the pancreas that has profound effects on carbohydrate, fat, and protein metabolism. Insulin deficiency results in hyperglycemia and other metabolic defects. The discovery of insulin in the 1920s by Banting and Best was a major medical milestone. Insulin is now manufactured recombinantly and comes in various rapid, short, intermediate, and long-acting forms to match physiological insulin secretion. Basal bolus regimens using basal and pre-meal bolus insulin are commonly used. New delivery methods like insulin pumps provide more flexibility but also challenges. Proper insulin storage and administration technique are important for effectiveness and safety.