Insulin misperceptions are specific, widespread, incorrect beliefs about the purpose, utility, and limitations of insulin. This article, the first of a series, attempts to define and classify insulin misperceptions, while providing an overview of their sources. It lists the target audience in whom misperceptions must be addressed, and differentiates between insulin-naïve and insulin experienced users, who may hold different misperceptions. The article provides a scientific framework with which to address insulin misperceptions in a rational, effective, manner.