The terms minimal change nephropathy and focal segmental glomerulosclerosis describe histopathological entities diagnosed by renal biopsy, typically in patients presenting with heavy proteinuria and its consequences including nephrotic syndrome. Numerous alterations in the immune response have been reported, but there is uncertainty about whether these play a causal role. In both conditions, there is evidence of injury to glomerular epithelial cells (podocytes), a cell type with limited potential for repair or replacement. The mechanisms of injury are poorly understood but may include immunologically mediated processes such as the effects of soluble mediators produced by lymphocytes. Empirical immunosuppressive therapy with corticosteroids, alkylating agents, and/or calcineurin antagonists is often effective, but the potential for toxicity of these drugs is enormous, and more specific forms of treatment are needed. The focus in recent years has been on the podocyte, and in particular the potential importance of mutations/polymorphisms in podocyte-specific genes as predisposing factors, mechanisms of podocyte injury including study of the role of podocytes as active participants in disease pathogenesis, indices of podocyte injury as markers of disease activity or possible diagnostic tools, and strategies for podocyte repair including the recognition that existing therapies may have effects (beneficial or adverse) on podocytes. Future improvements in the understanding of these diseases and in our ability to successfully treat them can be confidently expected as a result of rapid advances in the study of podocyte biology in health and disease.