Abstract Since the onset of the 1990s, the development of single-molecule spectroscopy has led to the discovery of various quantum optical signatures in organic single molecules. The single-photon nature of an organic chromophore is of particular importance because of its potential as a nonclassical photon source at room temperature for quantum information science and optical quantum computing. This condensed review focuses on the introduction of fundamental knowledge and basic experimental methods for single-photon sources and organic molecular photophysics and summarizes the research developments in this field, providing an understanding of quantum emission from organic single molecules.