Many materials have complex structural and dynamic properties intermediate between those of crystals and fluids. Among these are liquid crystals, with their well-known orientational order; colloids; polymer solutions and melts; foams; and gels; collectively these have come to be called "soft matter." These materials generally consist of organic molecules that interact weakly; as a result, thermal fluctuations, external fields, and boundary effects strongly influence their structure and properties. This sensitivity raises interesting new problems in basic physics, chemistry, and materials science; offers a path of thinking about some processes in biological systems; and opens numerous possibilities for technological applications. This textbook for graduate students in physics or chemical physics begins with a discussion of chemical bonds, interactions between particles, and the resulting molecular arrangements. The concept of order parameter leads to a discussion of phase transitions, elasticity and dynamics, followed by a review of fractals and growth phenomena. A significant portion of the book deals with defects of topological nature that accompany various types of order. The book concludes with chapters on surface phenomena, stability of colloidal systems, and structural properties of polymers. The detailed exposition, the emphasis on physical principles, and the exercises at the end of each chapter will make this book a valuable introduction for graduate students and researchers to this rapidly growing field.