Over the last decade major advances have been made in our understanding of how plants sense, signal and respond to soil phosphorus (P) availability. Shoot derived carbohydrates, in particular sucrose, have the potential to act as signalling molecules for plant responses to low P availability. Under P starvation, plants accumulate sugars and starch in their leaves. Increased loading of sucrose to the phloem under P starvation primarily functions to relocate carbon resources to the roots, increasing root biomass. The translocation of sugars via the phloem also has the potential to initiate sugar-signalling cascades that alter the expression of genes involved plant responses to low P availability. These include optimising root biochemistry to acquire soil P through increased expression and activity of inorganic phosphate transporters, the secretion of acid phosphatases and organic acids to release P from the soil and the optimisation of internal P use. Here we provide and update to the field of plant signalling responses to low P availability and the interactions with sugar signalling components. Advances in the P signalling pathways and the roles of hormones in signalling plant responses to low P availability is also reviewed, and where possible their interactions with potential sugar signalling pathways.