Anion- interactions, the counterintuitive cousins of cation- interactions, arise when an anionic species interacts with an aromatic surface possessing a positive quadrapole moment perpendicular to the aromatic plane. They remained largely overlooked 3 until their nature was delineated through molecular modelling in 2002. Since then, thanks to extensive efforts by many research groups, anionπ interactions are now recognised as important non-covalent interactions in both the solution-4 and solid-state, and evidence is emerging that they play a role in the structure and function of enzymes. Matile and co-workers coined the term anion-π catalysis to describe reactions that are accelerated by stabilizing anionic transitions states and intermediates through interaction with a catalyst containing a π-acidic aromatic surface. The anion-π catalysis concept has since been applied to a range of reactions, typically making use of electron deficient naphthalene diimides (NDIs) and their extended homologues or electron deficient heteroaromatic species, including enantioselective examples. More recently, examples have been reported in which the surfaces of fullerenes or carbon nanotubes display anion-π catalysis, as well examples in which an electron deficient π surface is engaged in π-π stacking interactions, the results of which, supported by computational analysis, suggest that the polarizability of the π surface, as well as its permanent quadrapole moment, plays a key role in catalyst activity.