The Raman spectrum of coumarin in the solid state and when dissolved in various solvents has been examined with reference to (1) the C=C and (2) the C=O frequencies. Of the three frequencies belonging to (1) which are fairly constant throughout, the two lower ones represent the aromatic double bonds of the benzene ring and the third represents the ethylene double bond of the pyrone ring. The C=O frequency is considerably low in the solid state as well as in the solutions with certain polar solvents. This is attributed to the weakening of the C=O bond by the formation of hydrogen bonds through co-ordination.