We use Green function techniques to calculate the electronic and optical properties of conjugated polymers, e.g. exciton binding energies, lifetimes, and polarizabilities, and optical gaps. Applications are on isolated chains, both in vacuum and solution, and on crystalline geometries; in some cases a model screening is used. We obtain agreement with a variety of experiments for polythiophene, poly(phenylene vinylene) and poly(para-phenylene). Including screening effects from the chain environment proves essential for this.