The kidneys perform diverse functions including excretion of nitrogenous waste products, homeostasis of water, electrolytes and acid–base balance, and hormone secretion. The simplest functional unit within the kidneys is the nephron, which consists of specialized segments from glomerulus, through proximal tubule, loop of Henle, and distal tubule. Human nephrogenesis starts with two stages of transient kidneys, termed the pronephros and mesonephros, and ends with development of a permanent organ from the metanephros on each side. The latter consists of just a few hundred cells when it is formed in the fifth week of pregnancy but progresses to a nephron endowment of between 0.6 to 1.3 million by the time nephrogenesis is completed at 32–36 weeks of gestation. Key events during this process include outgrowth of the epithelial ureteric bud from the mesonephric duct, interactions between the bud and the metanephric blastema (a specific region of mesenchyme) that cause the bud to branch and mesenchyme to condense, epithelialization of the mesenchyme to form proximal parts of the nephron, and differentiation of segment specific cells. Molecular control of these events is being unpicked with data from human genetic syndromes and animal models, and this chapter highlights several of the most important factors/systems involved. Increased understanding of development is not just relevant to congenital kidney malformations, but may also be important in designing rational therapies for diseases of the mature kidney where recapitulation of developmental pathways is common.