Type 1 diabetes (T1D) is an autoimmune disease in which T cells attack and destroy the insulin-producing β cells in the pancreatic islets. Genetic and environmental factors increase T1D risk by compromising immune homeostasis. Although the discovery and use of insulin have transformed T1D treatment, insulin therapy does not change the underlying disease or fully prevent complications. Over the past two decades, research has identified multiple immune cell types and soluble factors that destroy insulin-producing β cells. These insights into disease pathogenesis have enabled the development of therapies to prevent and modify T1D. In this review, we highlight the key events that initiate and sustain pancreatic islet inflammation in T1D, the current state of the immunological therapies, and their advantages for the treatment of T1D.