Prediabetes is an intermediate stage between normal glycemia and diabetes and is highly prevalent, especially in older age groups and obese individuals. Five different definitions of prediabetes are used in current practice, which are based on different cut points of HbA_1C, fasting glucose, and 2-h glucose. A major challenge for the field is a lack of guidance on when one definition might be preferred over another. Risks of major complications in persons with prediabetes, including diabetes, cardiovascular disease, kidney disease, and death, also vary depending on the prediabetes definition used. Randomized clinical trials have demonstrated that lifestyle and pharmacologic interventions can be cost-effective, prevent diabetes, and improve cardiovascular risk factors in adults with prediabetes. However, the practical implementation of lifestyle modification or the use of metformin for treating prediabetes is inadequate and complicated by a lack of agreement on how to define the condition. Establishing consensus definitions for prediabetes should be a priority and will help inform expansion of insurance coverage for lifestyle modification and improve current screening and diagnostic practices.