Membranous nephropathy is a major cause of nephrotic syndrome of non-diabetic origin in adults. It is the second or third leading cause of end-stage renal disease in patients with primary glomerulonephritis, and is the leading glomerulopathy that recurs after kidney transplantation (occurring in about 40% of patients). Treatment with costly and potentially toxic drugs remains controversial and challenging, partly because of insufficient insight into the pathogenesis of the disease and absence of sensitive biomarkers of disease activity. The disease is caused by the formation of immune deposits on the outer aspect of the glomerular basement membrane, which contain podocyte or planted antigens and circulating antibodies specific to those antigens, resulting in complement activation. In 2002, podocyte neutral endopeptidase was identified as an antigenic target of circulating antibodies in alloimmune neonatal nephropathy, and in 2009, podocyte phospholipase A2 receptor (PLA2R) was reported as an antigenic target in autoimmune adult membranous nephropathy. These major breakthroughs were translated to clinical practice very quickly. Measurement of anti-PLA2R antibodies in serum and detection of PLA2R antigen in glomerular deposits can now be done routinely. Anti-PLA2R antibodies have high specificity (close to 100%), sensitivity (70-80%), and predictive value. PLA2R detection in immune deposits allows for retrospective diagnosis of PLA2R-related membranous nephropathy in archival kidney biopsies. These tests already have a major effect on diagnosis and monitoring of treatment, including after transplantation.