Complex fluids can be found all around us, from molten plastics to mayonnaise, and understanding their highly non-linear dynamics is the subject of much research. This text introduces a common theoretical framework for understanding and predicting the flow behavior of complex fluids. This framework allows for results including a qualitative understanding of the relationship between a fluid's behavior at the microscale of particles or macromolecules, and its macroscopic, viscoelastic properties. The author uses a microstructural approach to derive constitutive theories that remain simple enough to allow computational predictions of complicated macroscale flows. Readers develop their intuition to learn how to approach the description of materials not covered in the book, as well as limits such as higher concentrations that require computational methods for microstructural analysis. This monograph's unique breadth and depth make it a valuable resource for researchers and graduate students in fluid mechanics.