The absorption and fluorescence spectra of seven sandwich dimers of substituted anthracenes are reported. The absorption spectra of dimers of 9‐methyl‐, 9‐chloro‐, 9‐bromo‐, and 9‐cyanoanthracene are consistent with a symmetrical sandwich configuration. The resonance splittings are about 400 cm−1for the1A1g→1B2utransition (of anthracene) and about 1500 cm−1for the1A1g→1B3utransition. The dimers of 9,10‐dichloroanthracene and 9,10‐dibromoanthracene have absorption spectra consistent with a rotated sandwich configuration; the angle between the molecular axes is 61 deg for the dichloro compound and 73 deg for the dibromo compound. The spectrum of the mixed sandwich dimer of anthracene and 9,10‐dichloroanthracene is interpreted on the basis of a ``symmetrical'' sandwich configuration. The1B3uelectronic states are completely mixed by orbital overlap and only one absorption band is observed. On the other hand the spectral features of both monomer transitions to the1B2ustate are present in the spectrum of the dimer. The fluorescence spectra of all the sandwich dimers are of the excimer type and the fluorescence yield, relative to that of the monomer, is decreased markedly by the heavy‐atom substituents. The relevance of the experimental results to the theories of the energy levels of dimers and excimers is discussed critically.