One-dimensional organic nanowires and nanoribbons represent idealized model systems for investigating charge transport mechanisms at molecular length scales. However, there are significant difficulties associated with the synthesis of organic nanowires and nanoribbons with precisely defined sequences, lengths, geometries, and terminal functionalities. By drawing inspiration from the structure of DNA and from automated oligonucleotide synthesis techniques, we have developed facile strategies for the covalent assembly of organic semiconductor building blocks into precisely defined one-dimensional ensembles. We have investigated the properties of these nanowires with a suite of spectroscopic, electrochemical, and computational techniques. Our findings hold significance both for fundamentally understanding nanoscale charge transport phenomena and for the development of new types of biological and molecular electronic devices.