In this talk I review the hierarchy problem, and I will describe recent progress in understanding the additional constraints that UV/IR mixing places on a theory that may be giving hints as to how it can be solved. As an example that can be treated rigorously, I will consider the UV/IR mixing associated with modular invariance in closed strings, and show that this yields a novel set of supertrace constraints. These constraints are similar to the nonrenormalisation theorems of supersymmetry but they are applicable in full generality. I discuss the various phenomenological consequences that arise including the lack of any power law running, and the apparent UV fixed-point behaviour. The talk will be pedagogical.