Intra- and intermolecular interactions in bithiophene are investigated via the measured and calculated vibrational density of states for the polycrystalline material. There is strong intermolecular interaction that hardens vibrational coordinates with respect to the isolated molecule, especially the inter-ring torsion. The torsional barrier of the isolated molecule is understood in terms of delocalization energy, nonbonded intramolecular interaction, but in the solid the barrier is dominated by intermolecular interaction. A topological analysis of the calculated electron density provides a local interpretation of intermolecular bonds that give rise to the intermolecular interactions. The results for this simple conjugated system are important for the extension to polythiophene and other conducting polymers.