This collection of essays devoted to Heinrich Hertz (1857-1894) brings together an international group of physicists, philosophers, and historians of science. It includes investigations of Hertz's background, his theoretical and experimental contributions, his philosophy of science, and his influence on science and philosophy in the 20th century. Its central focus is Hertz's 'Principles of Mechanics' of 1894, which develops the methodological intuitions that also informed his earlier discovery of electromagnetic wave radiation (so-called radio waves). Though his proposed reform of mechanics was not adopted, the book proved influential on physicists like Einstein, Schrodinger, Bohr, and Heisenberg, and on philosophers like Cassirer, Schlick, and Wittgenstein. It can be regarded as an ancestor of Thomas Kuhn's Structure of Scientific Revolutions, it anticipated current discussions on the role of models in science, and it represents an important chapter in the history of conventionalism.