Every person produces more than one liter of urine every day, which is formed by our kidneys. How does this organ work? On the one hand, kidneys dispose of toxins and waste, and on the other, they regulate the amount of fluid, salt and other nutrients the body needs. Kidneys also produce important hormones and therefore significantly influence bones and blood. We show how healthy kidneys manage to fulfill these different functions. But what happens when the kidneys get sick? For some time now, kidney function can be partially replaced by artificial filters (dialysis). Recently, it has even become possible to regrow kidney tissue in the laboratory. We are also working on artificially generating kidney cells. We explain how this is done and how patients with kidney disease could benefit from it in the future.