The relation between the crystallographic and electronic structures is discussed for single crystals and thin films of pentacene. The polymorphs of pentacene reported so far are reviewed with particular emphasis on the structural analysis of thin films using X-ray diffraction techniques. For the three different polymorphs of which the precise crystallographic structures are available, the band calculations are made using density functional theory. Band structures, effective masses and transfer integrals depend strongly on the crystallographic structures indicating a large difference in the transport properties. Only three transfer integrals are needed to describe the band structures in the framework of tight-binding approximation. By considering the relation between the transfer integrals and the crystal structure, the difference in the band structures can simply be explained by the different orientation angles of molecular long axis.
