Viscoelasticity is a complicated theorem that is generally used in several aspects of material characterization and modeling of polymers, resins, fiber-reinforced composites, bituminous composites, etc. On the other hand, the heterogeneous nature of composites like asphalt concrete and fiber-reinforced polymers has motivated lots of researchers to investigate the mechanical and rheological properties of these materials. This book mainly consists of the theory and application of viscoelastic materials used for construction. It starts with a comprehensible presentation of the theory of linear and nonlinear viscoelasticity. Wherein, the application of viscoelastic equations and principles on constructional viscoelastic composite materials considering time, temperature, loading rate dependency, and heterogeneity of composite substances is highlighted. The principles and equations of the viscoelasticity theorem are presented in several books, but here it is tried to present them more understandable and straightforwardly. This helps in solving real problems of heterogeneous composite materials, especially those which are used in construction. Moreover, the fundamental experiments for characterizing the elastic and viscoelastic properties of fibrous and bituminous composites are introduced and summarized. Then after, some analytical and empirical formulations for deriving the material properties of composites from the properties of the basic constituents are presented. These are followed by numerical simulation techniques using the finite element method to simulate composite materials.