A great variety of prokaryotic ribosomally synthesized and posttranslationally modified peptides (RiPPs) were predicted and identified experimentally owing to recent advances in large-scale genome sequencing and data analysis. Thiazole/oxazole-modified microcins (TOMMs) are a group of RiPPs that have characteristic thiazole and oxazole heterocycles derived from cysteine and serine residues. The review summarizes the available data on the classification, structure, and biosynthesis of TOMMs and discusses their biological activity and potential use in medicine.