Immunoglobulin A nephropathy (IgAN) is defined by the predominant deposition of IgA in the glomerular mesangium. Light microscopic appearances and clinical features can vary considerably, reflecting the many patterns of histopathologic injury seen in this glomerulonephritis (GN) Closely associated with IgAN is Henoch-Schönlein purpura (HSP), a smallvessel systemic vasculitis characterized by small blood vessel deposition of IgA predominantly affecting the skin, joints, gut, and kidney. The nephritis of HSP is also characterized by mesangial IgA deposition and may be histologically indistinguishable from IgAN. Both clinical and laboratory evidence support a close relationship between IgAN and the nephritis of HSP (1). This article focuses on IgAN considering especially new information available since IgAN was last reviewed in the Journal of the American Society of Nephrology (2). In particular, we focus on our growing understanding of the pathogenesis of IgAN, and we discuss the impact of recently published randomized, controlled trials (RCT) on recommended treatment strategies.