The question “What determines the smell of a chemical compound?” has long fascinated scientists. To this day, however, there is no definitive answer. The rapid development of organic chemistry at the end of the nineteenth century and chemists’ desire to synthesize new aromatic compounds for the perfume industry led to the first hypothesis about odors. This was proposed by the Dutch physiologist Hendrik Zwaardemaker (1857–1930) and emerged in 1876 under the influence of Otto Nikolaus Witt’s “chromophore theory.” According to this theory, the color of organic compounds is determined by functional groups known as chromophores. By analogy, in 1895 Zwaardemaker assumed that the odor of chemical compounds could be traced back to similar groups, which he called “osmophores” (from οσμή, osme, Gr.—smell, and φέρω, fero, Gr.—to carry). His hypothesis was therefore referred to as “osmophoric.” According to Zwaardemaker, whose theory was heavily criticized and rejected in 1920, osmophoric groups are -COOH, -COOR, -CHO, >C=O, -OH, and -NO2. In the mid-twentieth century, new hypotheses were added, and by the end of the century there were more than 40. The large number of hypotheses regarding a scientific problem is, firstly, an indication of public interest in it and, secondly, of its complexity. Based on experience so far, it is primarily organic compounds that have an odor, but inorganic substances such as the halogen elements fluorine, chlorine, bromine, and iodine also do. Ozone, phosphorus, arsenic, sulfur, selenium, and some of their compounds also have a smell.