A large number of lymphoproliferative and granulomatous conditions can be diagnosed in the oral cavity and gnathic bones. These lesions range from infectious (leprosy, histoplasmosis, leishmaniasis), locally reactive (biofilm-related gingivitis, allergic conditions, foreign body reactions), oral manifestations of systemic diseases (lupus erythematosus, Sjögren disease, sarcoidosis), to malignant neoplasms (lymphomas and leukemic infiltrations), thus representing a very heterogeneous group of disorders. Non-Hodgkin lymphomas are the most important lymphoproliferative diseases affecting the oral cavity, and pathologists need to be familiarized with the architectural and cytological findings that will lead to a correct diagnosis. However, differentiating a reactive from a neoplastic lymphoid infiltrate in the oral cavity may be very difficult. Therefore, a strict correlation between clinical data, microscopic findings, and immunohistochemical/genetic studies is paramount. This chapter will provide a detailed description and illustration of the epidemiological features of lymphomas and their main classification schemes proposed over time. Furthermore, it will also be provided a thorough description of important clinical, radiographic, and microscopic features that should be observed when dealing with lymphoproliferative and granulomatous disorders in the oral cavity and that will help pathologists and clinicians to achieve the correct diagnoses.