The statistical mechanical theory of liquids and solutions is a fundamental area of physical sciences with important implications in other fields of science and for many industrial applications. This book introduces equilibrium statistical mechanics in general, and statistical mechanics of liquids and solutions in particular. A major theme is the intimate relationship between forces in a fluid and the fluid structure - a relationship that is paramount for the understanding of the subject of interactions in dense fluids. Using this microscopic, molecular approach, the text emphasizes clarity of physical explanations for phenomena and mechanisms relevant to fluids, addressing the structure and behavior of liquids and solutions under various conditions. A notable feature is the author's treatment of forces between particles that include nanoparticles, macroparticles, and surfaces. The book provides an expanded, in-depth treatment of simple liquids and electrolytes in the bulk and in confinement. Provides an introduction to statistical mechanics of liquids and solutions with special attention to structure and interactions. Offers an extensive presentation starting with the basics of statistical mechanics to modern aspects of the theory of liquids and solutions, including intermolecular interactions in fluids. Treats both homogeneous bulk fluids and inhomogeneous fluids near surfaces and in confinement. Takes a microscopic, molecular approach that combines physical transparency, theoretical sharpness and a pedagogical and accessible style. Gives explicit and clear textual explanations and physical interpretations for any mathematical relationships and derivations. Goes deeper than the available texts on interactions in fluids, by taking the discussion beyond simple approximations and mean field approaches.The book will be an invaluable resource for advanced undergraduate, graduate, and postgraduate students in physics, chemistry, soft matter science, surface and colloid science and related fields, as well as professionals and instructors in those areas of science.