Glucagon gets a lot of mentions when we talk about diabetes. We take metformin to stop glucagon release; we inject glucagon when a patient is so hypoglycemic they are passed out. We even use glucagon-like peptide to treat diabetes. But exactly what is glucagon, where does it come from, and how does it work? This week our clinical text begins to look at this hormone, first discovered in 1923, and how glucagon research will lead to better diabetes care.