Membrane-spanning transport proteins are responsible for the selective passage of most mineral nutrients and metabolites across cellular and intracellular membranes. This review's focus is on summarising the current state of research covering the molecular regulation and biochemical mechanisms involved in the transport of phosphorus, an often growth-limiting nutrient, in vascular plants. Physiological data illustrating the tight control of Pi homeostasis on the cellular as well as on the organism's level are discussed together with the recent results on molecular transport mechanisms.