Pillarenes are macrocyclic compounds formed by the polymerization of aromatic monomers, with a rigid columnar structure and a hydrophobic cavity. They are used as supramolecular host materials because they are able to encapsulate guest molecules and form stable supramolecular assemblies through host-guest interactions. The size and shape of the pillarene cavity can be tuned by varying the number of aromatic rings in the macrocycle. Applications include catalysis, drug delivery, and separation of enantiomers. In supramolecular chemistry, pillarenes are used to prepare functional materials and explore novel host-guest interactions.