This document provides an overview of diabetes mellitus (DM), including the three main types (Type 1, Type 2, and gestational diabetes), signs and symptoms, complications, pathophysiology, oral manifestations, dental management considerations, emergency management, diagnosis, and treatment. DM is caused by either the pancreas not producing enough insulin or cells not responding properly to insulin, resulting in high blood sugar levels. The document compares and contrasts the characteristics of Type 1 and Type 2 DM.