p-Phosphonic acid calix[n]arenes and their O-alkylated lower rim analogues are remarkably versatile macrocycles, with applications in selective diameter uptake of single walled carbon nano-tubes, as surfactants in stabilising and protecting nano-particles and graphene sheets, as crystal growth modifiers for inorganic systems, in encapsulating molecules of anti-cancer carboplatin, self assembly into nano-arrays, including nano-fibres and molecular capsules, and for binding metal ions including biologically relevant Ca²⁺. They are readily accessible via five or six high yielding steps from the parent p-Bu^t substituted compounds.