This book bridges the gap between theoretical rheology and industry applications by utilizing the widely adopted and scientifically validated Control Theory (CT) to analyse and model various types of viscoelastic flows and macromolecular structures. In practical engineering, the design of machinery and equipment for polymers often relies on handbooks, respective textbooks, and numerous CAD-aided software tools based on empirical formulas. The original theories of viscoelasticity in rheology, with their main principles developed over a century ago, are rooted in spring-and-dashpot elements. Furthermore, many books and studies in theoretical rheology attempt to dissect all the variables of a polymer or viscoelastic flow in accordance with the principles of sound physics practice. This leads to a quagmire and complicated formulas without practical use. And still not possible variables effected by material structure is included. In the CT principle, this is achieved in a novel way and applied to the linear Unified Model—referred to as the Characteristic Model in a published paper—for different viscoelastic flows.