Supramolecular chemistry is the field of research dedicated to studying how molecules recognize each other, assemble and function on a molecular scale. It is an area of continuous interest and basically relies on the comprehension of a great deal of noncovalent interactions described in the literature. Among them, the anion–π interaction, i.e., the non-covalent force between an electron-deficient π-system and an anion, has increasingly been attracting attention since 2002. This chapter is devoted to the description of interesting and remarkable supramolecular assemblies, receptors and molecular containers where the anion–π interaction has a prominent role in both the solid state and solution. The impact of the anion–π interaction in solution is limited but not negligible and, conversely, the number of manuscripts describing supramolecular assemblies where this interaction plays a key role in the solid state has increased exponentially over the last five years. Herein we firstly describe the physical nature of this non-covalent interaction and secondly, we selected state-of-the-art reports illustrating the rational utilization of anion–π interactions in supramolecular chemistry, both in solution and solid state.