The Collected Works of Irving Langmuir: Volume 6, Structure of Matter deals with the research work of Irving Langmuir in the field of thermionics, gaseous discharge, and on the structure of atoms with emphasis on valence. Some of the paper he writes on the subject of atomic structure are: "The Structure of Atoms and the Octet Theory of Valence," "The Arrangement of Electrons in Atoms and Molecules," and "The Octet Theory of Valence and its Applications with Special Reference to Organic Nitrogen Compounds." He challenges the complexities of valence theory and atomic structure, leading to a complete change of the theoretical structure of the subject of chemistry. Langmuir also works on molecules and crystalline structures, and applies the structures of crystals to check and confirm his own theories on molecular structure. His assumption that "the force between molecules in contact can be considered as caused by a surface energy proportional to the area over which the molecules are in contact" provides a solid foundation for explaining the properties of many chemical substances. Chemists, students, academicians, scientists, and general readers interested in the lives of great men in science will find this book very informative.