Recent studies have emphasized the critical role of podocytes for the size-selective filtration barrier of the kidney and revealed novel aspects of the mechanisms leading to proteinuria, both in inherited and acquired diseases. It has been shown that a specialized cell junction, the slit diaphragm, connecting neighboring podocytes, is of critical importance to the development and the integrity of the glomerular filter. Several critical structural protein components of the slit diaphragm have been identified. In addition to their structural functions, these proteins participate in common signaling pathways. This talk will focus on what is known about the importance of the podocyte for the function of the glomerular filter of the kidney. It will provide a snapshot of our current understanding of the signaling properties of slit diaphragm proteins and project a framework for further studies necessary to delineate the function and dynamics of the slit diaphragm protein complex and the pathogenesis of nephrotic syndrome.