The book focuses on electromagnetic absorbing and shielding properties of multilayer materials. Nanomaterials are widely used and composite materials? dielectric characterization is deeply discussed. Very little academic literature exists on how to model(design) an electromagnetic absorber using matrix formalism of microwave propagation through multilayer materials. This book therefore, provides an interesting approach to the absorber?s design in which different branches of science are applied and where all of them are used to optimize the ?quasi perfect absorber?: nanotechnology, electromagnetic wave propagation theory, composite materials manufacturing, evolutionary computation. With respect to the present literature, the method presented in this book computes the absorbing capability of materials, taking into account for the reflection and transmission coefficients, considering also oblique incidence of the electromagnetic field. Theoretical modeling of absorbers is experimentally validated. At the end of the book the electromagnetic shielding performance of carbon-carbon material and of high weight percentage carbon nanotubes based composite materials are throughly analyzed.