The spleen is an organ in the upper far left part of the abdomen, to the left of the stomach. The spleen varies in size and shape between people, but it’s commonly fist-shaped, purple, and about 4 inches long. Major functions of spleen are filtration function, immunologic function, hematopoiesis function, and reservoir function. Indications for splenectomy, causes of splenic reactive follicular hyperplasia, splenic lymphomas, hematopoietic neoplasms (involve spleen), splenic B-cell marginal zone lymphoma, splenic diffuse red pulp small B-cell lymphoma, and hepatosplenic T-cell lymphoma are also covered in this chapter.