The pedagogically presented lectures deal with viscoelastic behaviour of fluids, the compatibility of rheological theories with nonequilibrium thermodynamics, fluids under shear, and polymer behaviour in solution and in biological systems. The main aims of the book are to stress the importance of the study of rheological systems for statistical physics and nonequilibrium thermodynamics and to present recent results in rheological modelling. The book will be a valuable source for both students and researchers.