This paper discusses the basic theoretical problems that are present in rubber technology. Today tires are formed from a multitude of different components. For example, tread compounds of automotive tires consist of various different components, such as blends of homo- and/or copolymers, plasticizers, and fillers. The thermodynamic and physical interactions of these components present challenging problems for polymer physicist. First steps on deriving structure - property relationships from molecular models are presented. Examples will be the polymer -filler interactions of the different components, their effect on reinforcement, and the thermodynamic behavior of the different components themselves.