Diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) are the most common histological types of B-cell lymphoma, but have significantly different pathological and biological characteristics. In recent years, understanding of the genetic abnormalities and microenvironmental structures of these lymphomas has progressed, and various molecular targeted drugs and immunotherapies have been introduced into clinical practice. Therefore, accurate understanding of etiology and its clinical relevance is required for the appropriate management of these lymphomas.