A study of the polarized infrared and Raman spectra of acenaphthylene single crystals has been made. These results, together with Gordon and Yang's preliminary X-ray work, suggest that the molecules pack in some disordered arrangement in the solid at room temperature. Most of the A1 fundamentals were identified in the Raman solution spectrum from their low depolarization ratio, and a few tentative assignments of nontotally symmetric fundamentals were made.