Ever since the evolution of nanofibers and nanotubes in 80's & 90's there has been significant revolution in the field of materials with nano materials coming into foray compared to conventional materials. Embedded in traditional polymers the nano materials are marking their trend in the field of composites and are competitively used in aerospace and automotive industries. The research front in the field of nanocomposites is divided into experimental and theoretical. Though experimental means is the best way to develop a material's application, a theoretical base is also required to establish the science of experiments. To respond to this need, this book presents several models in the prediction of elastic modulus of nanocomposites and the resulting stiffness matrix. In today's world, every structure designed involves uncertainty. eterministic approaches employed to meet the design criteria often involves inefficient design raising the design cost. To reduce the costs and also the uncertainty in failure a new risk-based reliability approach has to be used. To meet these ends this book also focuses on probabilistic approach of engineering nanocomposites.