Renal involvement is common in patients with systemic lupus erythematosus. Light microscopic features of glomeruli in lupus nephritis are diverse from normal to focal and diffuse proliferative, to membranous thickening of glomeruli and frequently associated with variable degrees of tubulointerstitial and vascular lesions. Immune deposits consisting of various immunoglobulins and complements could be observed in glomeruli as well as tubular basement membranes and vessels. However, the kidney may be injured by non-immune mechanisms as well. It is important to know the extent and degrees of renal involvement for clinicians to build therapeutic plans and predict renal survival. Histologic assessment of glomerular lesions in lupus nephritis has evolved from the WHO classification, which was published in 1975 and has been modified in 1980s. Activity and chronicity indices were proposed from NIH studies. The ISN/RPS classification, which is currently used, was developed under the auspices of ISN and Renal Pathology Society and published in 2004. In this session, I will summarize histologic features of the ISN/RPS classification of lupus nephritis and controversial issues related to this classification.