Phosphorus (P) scarcity and the need for ecologically sound intensification of agroecosystems are major challenges we face. To improve nutrient efficiency in agriculture, especially for P, multispecies crop stands may outperform their monospecific counterparts, especially under low input conditions. There is increasing evidence that biomass, grain yield and nutrient acquisition are improved in cereal/legume intercropping systems, relative to cereal or legume grown alone. Hereafter, we consider these observations, outline the underlying mechanisms, and examine recent work that advances our knowledge of how cereal/legume intercropping systems acquire P in their rhizospheres, through various types of positive belowground-interactions. First, we discuss how complementarity may operate when cereals are intercropped with legumes by addressing cases of complementary use of soil P resources in space and time, and showing how functionally diverse intercropped species can use different pools of soil P. Then we address examples of facilitation, i.e. positive interactions between two intercropped species, in which the legume (or cereal) may increase P availability for the benefit of the intercropped cereal (or legume). Finally, the relevance of a range of root-induced or microbially-mediated rhizosphere processes driving P acquisition are discussed.