While other azole heterocycles are prevalent in a wide variety of bioactive natural products, the imidazole ring occurs frequently in the context of the natural amino acid histidine. Additionally, the imidazole ring occurs as a component of unnatural cyclic peptides and is used as an ester isostere in peptidomimetic studies. The applications of imidazole are not limited to the realm of peptides and peptidomimetics. Imidazoles are present in the large family of bromopyrrole-imidazole alkaloids isolated from marine sponges based on the common metabolite oroidin that feature significant biological activities. The imidazole ring also appears in the pilocarpine alkaloids, as well as potential therapeutic agents for thrombosis, cancer, and inflammatory diseases.