Type 1 diabetes mellitus is characterized not only by insulin deficiency, but also dysregulation of endogenous glucagon secretion. Impaired glucagon response to hypoglycemia renders the person with diabetes prone to severe hypoglycemia and represents one of the major impediments to achieving optimal glycemic control and quality of life. Due to instability of recombinant glucagon in liquid form, until now the only roles of subcutaneous glucagon in the treatment of type 1 diabetes have been as rescue for severe hypoglycemia, and less commonly, mini-doses for prevention of hypoglycemia during acute illness or exercise. The recent availability of liquid-stable glucagon has enabled the development of improved methods to treat and/or prevent hypoglycemia, as well as raised the possibility of feasible dual-hormone artificial pancreas systems. This presentation will highlight key studies demonstrating the importance of glucagon in successful management of type 1 diabetes, both as a standalone drug and as part of a dual-hormone system.