The onset of heat waves can be subtle and do not result in structural damage like many other meteorological events. Components to consider that comprise a heat wave include: duration, daytime high and overnight low temperatures, atmospheric moisture, human impacts, and location. Nonetheless, even with these deterministic factors, heat waves lack a meaningful uniform meteorological definition. This talk will focus on what constitutes summer heat waves in the Midwest by identifying the thresholds of high temperature that are representative of the most extreme events. Heat waves will be classified based on surface observation records from select large urban areas of the Midwest (i.e., St. Louis and Columbus). The large-scale weather features and high moisture conditions will be examined for the events to categorize consistent patterns. In addition, any changes manifest in the number and duration of past heat waves will be presented. The historical significance and characteristics of the most extreme heat waves on record will also be discussed.