Type 1 diabetes is characterized by an absolute deficiency of insulin due to the autoimmune destruction of pancreatic beta cells. It typically presents in childhood or early adulthood with symptoms of polyuria, polydipsia, and unexplained weight loss. Treatment involves lifelong insulin replacement therapy via injections to control blood glucose levels and minimize the risk of complications. Rapid-, short-, intermediate-, and long-acting insulin formulations have different onset and duration profiles suited to individual treatment regimens. Strict glycemic control is important to reduce microvascular and macrovascular risks.