The hyperpolarizabilities of a series of donor-acceptor azothiophene dyes have been assessed experimentally for the linear electrooptic effect (LEO) using a solvatochromic technique and theoretically using both a sum-over-states approach at the CNDO/S level and a time-dependent coupled Hartree-Fock approach at the AM1 level. Reasonable correlations have been found between the magnitude of the experimental beta(xxx) values from solvatochromic measurements and those calculated, All the azothiophenes examined possess large values which are substantially greater than those obtained for related azobenzenes. There is substantial resonance enhancement of the hyperpolarizabilities of the phenylazothiophenes when the phenyl ring is replaced by a naphthalene ring because of a lowering of the transition energy between the ground and first excited state. The naphthylazothiophenes have very large hyperpolarizabilities coupled with large dipole moments, which make them ideal candidates for applications in poled polymer films as LEO modulators.