A novel thin film processing technique has been developed for the fabrication of ultrathin films of conducting polymers with angstrom-level control over thickness and multilayer architecture. Molecular self-assembly of in-situ polymerized conjugated polymers consists of a layer-by-layer process in which a substrate is alternately dipped into a solution of a p-doped conducting polymer (e.g. polypyrrole, polyaniline) and a solution of a polyanion. In-situ oxidative polymerization produces the more highly conductive, underivatized form of the conjugated polymer, which is deposited in a single layer of precisely controlled thickness (30 to 60 Å). The thickness of each layer can be fine-tuned by adjusting the dipping time and the solution chemistry. The surface chemistry of the substrate (e.g. hydrophobic, charged, etc.) also strongly influences the deposition, thereby making it possible to selectively deposit conducting polypyrrole onto well defined regions of the substrates. Typical multilayer films exhibit conductivities in the range of 20–50 S/cm, but samples with conductivities as high as 300 S/cm have been realized. There is no limit to the number of layers that can be built up nor to the complexity of the multilayer architecture of the film; achieved simply by alternating the sequence of dips into solutions of various polycations and polyanions. This new self-assembly process opens up vast possibilities in applications which require large area, ultrathin films of conducting polymers and, more importantly, in applications that can take advantage of the unique interactions achievable in the complex, supermolecular architectures of multilayer films.