Thermal conductivities represent one of the most important properties of polymer and elastomer materials that determine their final use in industry and research. Therefore, there exists a great interest to understand the inherent structure-property relations between the molecular structure and the thermal conductivity. The review summarizes approaches to calculate thermal conductivities ranging from macroscopic to microscopic level, whereas it is generally accepted that an appropriate design of new materials with optimized thermal properties is only accessible via knowledge-based bottom-up approaches. Both approaches – macroscopically and microscopically based – are presented in retrospect with their historical development. Supplementary to the theoretical view elaborated experimental methods are described with the focus on elastomers.