Acute, granulomatous and chronic are the three main forms of gastritis. The discovery of Helicobacter pylori has stimulated a new detailed classification of gastritis. Having set out the various conventional histopathological classifications, the authors describe two newly recognized types of gastritis, lymphocytic gastritis and reactive gastritis. The authors also recall the earlier pathogenic classifications of gastritis, first initiated by Strickland and Mackay. Because of the problems related to these earlier classifications, the "Sydney system" has been developed. This system allows to simply pathologists' reports, by incorporating the morphological, topographical and etiological parameters of gastritis. Some of the advantages and disadvantages of the "Sydney system" are briefly discussed.