**1. Introduction**

Lupus nephritis (LN) is the most common severe organ manifestation of systemic lupus erythematosus (SLE). It may be the presenting manifestation of SLE and usually arises within 5 years of diagnosis [1]. Approximately 40–70% of SLE patients will develop LN [2] with histopathological changes observed in most patients even among those without renal manifestations (known as "silent LN"; mostly with "milder" class I and II histologic lesions) [3, 4]. Clinical presentation of LN is highly variable, ranging from asymptomatic proteinuria with normal renal function to rapidly progressive renal failure.

Recent data demonstrates reduction in the temporal mortality trend among end stage renal disease (ESRD) LN patients [5]; however, the risk of progression to ESRD in LN remains unchanged [5, 6]. Despite significant improvement of outcome in this modern era, less than 50% of patients achieve complete clinical remission following immune suppression [7] with 10–20% of patients progressing to ESRD [8]. This chapter explores recent studies that have substantially contributed to our understanding of LN and provides new insights into the epidemiology, pathogenesis, classification criteria and management strategies of LN.
