Lymphoma is a group of neoplastic disease of lymphoid tissues, which can be classified into categories of Hodgkin's disease and non-Hodgkin's lymphoma(NHL). Prognosis of lymphoma depends on the extent of disease(staging) especially in Hodgkin's disease, but also depends on the histologic make up in non-Hodgkin's lymphoma. Although non-Hodgkin's lymphoma is a neoplastic transformation of lymphoid cell it is a collection of disease with merphologically and immunologically diverse make up. Consequently the classification of NHL has changed frequently and evolved according to the progress of immunologic and molecular knowledge added to the original morphologic classification. Lymphoma is a disorder sensitive to chemotherapy which often leads to cure of the disease even in advanced stage, while many other patients die from the progression of disease. Therefore, better understanding in newer classification and sensitive imaging technique, such as PET, in lymphoma will likely lead to the improvement of survival rate.