Lichen extracts or their purified compounds are invaluable biomaterials with both commercial and traditional applications. In lichen systematics, chemotaxonomy is commonly employed, primarily relying on metabolites. Fourier transform infrared (FTIR) spectroscopy is a powerful analytical technique for identifying chemical compounds in various materials. This study aimed to evaluate its ability to differentiate between lichen taxa and detect their chemical constituents. FTIR spectra were obtained in the mid-infrared region using intact lichen samples belonging to 29 species from 12 genera, utilizing a large sample size with the specimens collected from a limited geographical area. Spectral data were classified using unsupervised and supervised multivariate chemometric methods. Additionally, detailed peak assignments were made, enabling a comparative analysis of chemical constituents across different lichen genera. The FTIR spectra of lichens provided information regarding their major biomolecules, including lipids, proteins, carbohydrates, lactones, and lichen metabolites. Almost all the taxa included in this study were differentiated from one another, forming distinct clusters through chemometric analyses. Our approach demonstrated and extended the potential of FTIR spectroscopy as a tool in lichen chemotaxonomy. Classification patterns showed excellent consistency with their phylogenetic relationships. Moreover, it was confirmed that detecting specific lichen substances with marker peaks is feasible using this method. The proposed method may have applications in ecological and taxonomical research, as well as in industrial processes that use lichens as raw biological material. This paper presents the most comprehensive study on the use of FTIR spectroscopy to characterize and classify lichens, serving as a reference work for future research. Keywords: Chemometrics; Chemotaxonomy; Fingerprinting; FTIR spectroscopy; Lichen; Usnic acid; Vibrational spectroscopy.