The ultraviolet spectra of the acridone alkaloids and some derivatives have been studied. The various bands in the spectra of these compounds are interpreted by starting with theoretical treatments of the spectrum of anthracene and tracing spectral changes through acridine and phenazine to acridone. An interesting relation between the π-electron density of a given position in the acridone ring and the shift in wavelength of absorption bands due to an alkoxyl derivative is noted and the spectra of the alkaloids are shown to comply with this relationship. Compounds containing a 4-hydroxy-10-methylacridone structure are found to have unusual spectra and a possible explanation of this is proposed.