The properties (electronic, optical, mechanical and thermal) of organic semiconductors are strongly dependent on the chemical structure, configuration, conformation and relative position of the component molecules or molecular segments. Predicting the impact of structure on properties requires a detailed understanding of molecular dynamics and interactions at an atomistic level, as well as a computationally efficient means of translating structural information into optoelectronic properties at a macroscopic, device relevant level. Although predictive models are not yet available except for simple systems, significant progress has been made toward this goal, making use of multi-scale modeling techniques, coarse graining approaches, and structural measurements of model material systems. In this talk we will review methods used to simulate the structure – property relationship in organic semiconductors, and will present combined experimental and theoretical studies of a number of model systems including disordered and multicrystalline small molecular and conjugated polymer films. We investigate the extent to which coarse grained methods can be used to rationalize the electronic properties of such systems. We discuss the factors that influence the design of high performance organic semiconductors.