This document provides guidelines from the American Diabetes Association for classifying, diagnosing, and screening for diabetes. It defines the main types of diabetes and recommends using A1C, fasting plasma glucose, or oral glucose tolerance tests to diagnose diabetes and prediabetes. It provides testing guidelines for gestational diabetes, cystic fibrosis-related diabetes, monogenic forms of diabetes, and screening recommendations for different populations. The guidelines are based on reviews of the latest scientific evidence and aim to improve diabetes classification and diagnosis.