Imidazole (ImH) has the chemical formula C3N2H4 and exists as a white or colorless solid which is capable of dissolving in water and forming a mildly alkaline solution. As an aromatic heterocycle, it belongs to the diazole class of organic compounds and has meta-substituted nitrogen atoms that are non-adjacent to each other.

With its planar 5-membered ring structure, imidazole exhibits two equivalent tautomeric forms due to the ability of hydrogen to bind to either of its nitrogen atoms. Imidazole is a compound of high polarity, as demonstrated by its electric dipole moment of 3.67 D, and it is readily soluble in water.

Imidazole exhibits amphoterism, meaning that it can function as both an acid and a base. When it acts as an acid, the nitrogen-bound proton of imidazole is acidic with a pKa of 14.5, which makes it less acidic than carboxylic acids, phenols, and imides, but slightly more acidic than alcohols.

Imidazole is an aromatic five-membered molecule that comprises of two nitrogen atoms within the ring structure. One of the nitrogen atoms exhibits pyrrole-type behavior, while the other closely resembles a pyridine-type nitrogen.

Many important biological compounds contain imidazole, with the most common example being the amino acid histidine, which features an imidazole side-chain. Histidine is a constituent of numerous proteins and enzymes, where it binds metal cofactors, as observed in hemoglobin.