Diffusion is as central to our daily lives as it is to the chemical industry. It is a spontaneous mixing process basic to such diverse phenomena as transport in living cells, the efficiency of distillation, and the dispersal of pollutants. This second edition of a highly acclaimed text provides a clear and complete description of diffusion in fluids. It retains the features that won praise for the first edition - informal style, emphasis on physical insight and basic concepts, and lots of simple examples. The new edition offers increased coverage of unit operations, with chapters on absorption, distillation, extraction, and adsorption. New chapters on membranes and drug release broaden the book's scope. The entire text is extensively illustrated, and many new worked examples and homework problems have been added. This exceptionally clear and inviting text on diffusion will be used by students of engineering, chemistry, and life science.