Insulin is commonly seen as a response to blood glucose whose primary role is to keep blood glucose within a narrow range. This view of insulin fails to account for its many roles outside of energy metabolism that govern long-term investments in health. The biochemistry and physiology of insulin secretion suggest, rather, that insulin is a gauge of short-term energy status and energetic versatility. Since glucose can only be stored in small amounts and since it is the most versatile of the macronutrients in its ability to support specialized pathways of energy metabolism, it makes sense that it would be wired to the pancreas as the primary signal of short-term energy status and energetic versatility. In this lesson, we review the unique uses of glucose and the mechanisms of insulin signaling to synthesize them into a more nuanced view of the role of insulin than is typically presented.