Understanding the structural and thermodynamic properties of surfaces, interfaces, and membranes is important for both fundamental and practical reasons. Complex fluids and solids, important in the development of new materials, cannot be designed using trial and error methods due to the multiplicity of components and parameters. While these materials can sometimes be analyzed in terms of microscopic mixtures, it is often conceptually simpler to regard them as dispersions and to focus on the properties of the internal interfaces found in these systems. The basic physics centers on the properties of quasi-two-dimensional systems embedded in the three-dimensional world, thus exhibiting phenomena which do not exist in bulk materials.This approach is the basis behind the theoretical presentation of Statistical Thermodynamics of Surfaces, Interfaces, and Membranes. Focusing on the large-scale properties of these systems, these notes are meant to supplement the usual treatments in books on colloid and interface science. The approach adapted here first presents the traditional approach and then investigates throughout to treat the rich diversity of phenomena investigated in the field of colloid and interface science such as interfacial tension, the roughening transition, wetting, interactions between surfaces, membrane elasticity, and self-assembly. The presentation is that of a set of lecture notes (used in graduate courses taught by the author) including worked examples and further problems. This book is aimed at physicists, physical chemists, chemical engineers, and materials scientists who are interested in the statistical mechanics that underlie the macroscopic, thermodynamic properties of surfaces, interfaces, and membranes.While the primary focus of the book is on the systems important in colloid and interface science, a more general goal is to introduce the reader to several theoretical methods that are useful in applications of statistical mechanics to materials. It is thus the hope that the depth and breadth of coverage will introduce the condensed matter physicist to colloid science and present to the physical chemist or material scientist, who may already be familiar with the underlying phenomena, a modern theoretical perspective.