A historical account of highly ambitious attempts to understand all of nature in terms of fundamental physics. Presenting old and new 'theories of everything' in their historical contexts, the book discusses the nature and limits of scientific explanation in connection with concrete case studies. Helge Kragh is one of our best historians of physics, and the author of several outstanding books. The idea of a history of highly speculative theories in physics is excellent. Although there are popular accounts of recent cosmological and grand-unifying theories, no historian has so far attempted to bring together old and new cases of such theories. The result makes fascinating reading and induces thought-provoking comparisons.