Gingivitis and periodontitis are common gum diseases that affect many adults. Gingivitis happens when plaque, a sticky film of bacteria, builds up around the gums and causes them to become red, swollen, and prone to bleeding. If this inflammation is not treated, it can progress to periodontitis, a more serious condition where the bone and tissues that support the teeth begin to break down. This chapter explains how these diseases develop, what signs to look out for, and the factors that can increase risk, such as poor oral hygiene, smoking, and certain health conditions. It also outlines how gum disease can be prevented and managed through everyday care and professional dental treatment.