Based on lecture notes from the School on Rheology of Complex Fluids, this book discusses how to understand multicomponent-multiphase systems of which most of complex fluids are examples. The book covers a wide variety of application areas.The aim of the School on Rheology of Complex fluids is to bring together young researchers and teachers from educational and R&D institutions, and expose them to the basic concepts and research techniques used in the study of rheological behavior of complex fluids. The lectures will be delivered by well-recognized experts. The book contents will be based on the lecture notes of the school.Background.- Non-Newtonian Fluids: An Introduction.- Fundamentals of Rheology.- Mechanics of Liquid Mixtures.- Rheology.- Oscillatory Shear Rheology for Probing Nonlinear Viscoelasticity of Complex Fluids: Large Amplitude Oscillatory Shear.- PIV Techniques in Experimental Measurement of Two Phase (Gas-Liquid) Systems.- An Introduction to Hydrodynamic Stability.- Applications.- Statics and Dynamics of Dilute Polymer Solutions.- Polymer Rheology.- Active Matter.- Mathematical Modelling of Granular Materials.