Plants have evolved an array of responses that adapt their growth to conditions of limited phosphate (Pi) supply. These involve biochemical and developmental changes that improve Pi acquisition and recycling, and protect against the stress of Pi starvation. The induction of these responses requires a sophisticated regulatory system that integrates information on external and internal plant Pi status and the details of this regulatory system are only just beginning to be elucidated. In this review, the current knowledge of this regulatory system is summarized, the hallmark of which is the central role of transcription factor PHR1 in the co-ordinated regulation of many phosphate-starvation-responsive genes. The role of hormonal signalling is also described, including auxins, ethylene and, particularly, cytokinins in the regulation of Pi-starvation responses.