ABSTRACT. The Langmuir-Blodgett technique has recently been used to manipulate a variety of electroactive conjugated polymers into multilayer thin films with well defined layered structures and ordered molecular organizations. Multilayer thin films have been successfully fabricated from amphiphilic conjugated polymers and their precursors and from non-surface active conjugated polymers. In most cases, the molecular organizations of these films have been found to be highly anisotropic. The structures of these films have been probed by high energy synchrotron radiation, reflection-absorption infrared and low angle x-ray diffraction techniques. Electrical measurements have also revealed highly anisotropic behavior with the in-plane conductivities of these multilayer structures typically being many orders of magnitude greater than their transverse conductivities. The unique layered structures of these films, in some cases, have also been shown to give rise to unusually large dielectric constants over a wide frequency range. In this chapter, the fabrication, characterization and electrical properties of these new thin film multilayer structures are discussed. . IntroductionOver the past few years, the practice of molecular engineering has guided the design and synthesis of new electroactive polymers and has provided a deeper understanding of the structure-property relationships active in this very interesting class of materials. Molecular engineering in the simplest sense simply involves the manipulation and control of the physical and electronic properties of polymeric materials by suitable modifications of their molecular structures. Through this approach, it is possible to systematically alter the electrical, optical, mechanical and processing properties of electroactive polymers with the ultimate goal being the creation of materials with a collection of properties optimized for a particular technological application or scientific endeavor. The logical extension of this molecular manipulation approach is the development of techniques that provide control over the molecular and supermolecular organizations of these newly synthesized molecules. The net result would be an ability to design and fabricate complex molecular assemblies with controllable molecular architectures and well defined molecular arrangements. One could further envision the creation of multicomponent molecular assemblies in which each component serves a specific well defined function and is 363 J.L.