Henri Poincaré's 'The Foundations of Science' contains three extraordinary individual works of the philosophy of science from the early twentieth century: 'Science and Hypothesis', 'The Value of Science' and 'Science and Method'. Poincaré was an outstanding scientist who, writing on a whole array of scientific and mathematical topics, advocated intuition and prediction as well as experiment and explanation, the value of non-Euclidean geometries and the relativity of space, thus laying the groundwork for the Einsteinian revolution in physics. This new edition of Halsted's authorized translation from the original French has been carefully hand-edited and re-indexed to be clear and complete.