This chapter gives the brief description on gingival inflammation. Pristine gingiva is a state of super health where normal gingiva is free from significant accumulation of inflammatory cells. Hence histologically it may be described as pristine gingiva. Inflammation of gingiva is termed as gingivitis. The American Academy of Periodontology (AAP) defines gingivitis as an inflammation confined to the tissues of the marginal gingiva. The plaque microorganisms can exert its effect on periodontium by releasing certain products (e.g. collagenase, hyaluronidase, protease, chondroitin sulfatase), which can cause damage to the epithelial and connective tissue constituents. This chapter covers the initial lesion of stage I gingivitis, the early lesion of stage II gingivitis, the established lesion of stage III gingivitis, the advanced lesion of stage IV gingivitis, and progression from health to periodontitis.