With this book, Elliott Lieb joins his peers Hermann Weyl and Chen Ning Yang. Weyl’s Selecta was published in 1956, Yang’s Selected Papers in 1983. Lieb’s "Selecta", like its predecessors, gives us the essence of a great mathema- tical physicist concentrated into one convenient volume. Weyl, Yang and Lieb have much more in common than the accident of this manner of publication. They have in common a style and a tradition. Each of them is master of a for- midable mathematical technique. Each of them uses hard mathematical ana- lysis to reach an understanding of physical laws. Each of them enriches both physics and mathematics by finding new mathematical depths in the description of familiar physical processes. The central theme of Weyl’s work in mathematical physics was the idea of symmetry, linking physical invariance-principles with the mathematics of group-theory. One of Yang’s central themes is the idea of a gauge field, linking physical interactions with the mathematics of fibre-bundles. The central theme of Lieb’s papers collected in this book is the classical Thomas-Fermi model of an atom, linking the physical stability of matter with the mathematics of func- tional analysis. In all three cases, a rather simple physical idea provided the starting-point for building a grand and beautiful mathematical structure. Weyl, Yang and Lieb were not content with merely solving a problem. Each of them was concerned with understanding the deep mathematical roots out of which physical phenomena grow.