The pancreatic β-cell is responsible for producing and secreting insulin, a critical hormone which keeps blood glucose within a narrow physiological range throughout the day. Owing to its unrivaled role in insulin secretion, the KATP channel has been intensely studied over the last 35 years, and numerous gain- and loss-of-function mutations have been identified in patients throughout the KATP channel genes which cause insulin secretion disorders. However, in the absence of a 3D structure of the channel complex, fundamental aspects of KATP channel biology have remained a mystery. Specifically, where do sulfonylureas bind and how do they inhibit KATP channel activity to stimulate insulin secretion? Our group has also shown that these inhibitors can overcome the folding and/or trafficking defects of a specific class of loss-of-function mutations in the KATP channel which cause potentially life-threating hypoglycemia. In this dissertation I describe my efforts to answer these questions by solving moderate to high resolution structures of the channel complex by cryo-electron microscopy, which illuminate how physiological and pharmacological ligands impact channel behavior and inform an overall gating mechanism.