Baruch Spinoza places freedom as the ultimate aim and central value of the life well lived. His philosophy is marked by the most thorough going naturalism of any of its period, so much so that a number of its central tenets remain a matter of lively debate today.Spinoza's commitment to the search for a comprehensive understanding of all things inspired Einstein. Furthermore, discoveries in the neurosciences in the early twenty-first century provide evidence that Spinoza's biological understanding of the emotions may also have been essentially on target. It was upon this prescient naturalistic scientific foundation that Spinoza developed a new approach to ethics. Perhaps the most important heirs to Spinoza's thought are Nietzsche, Marx, and Freud, but the Radical Enlightenment has recently been laid largely at his feet. Nevertheless, Spinoza's last words in the Ethics sound a note of caution and perhaps even of warning: "All things excellent are as difficult as they are rare." Time, however, is finally catching up with Spinoza and the journey through his philosophy is well worth the effort, as his views now more than ever capture the contemporary scientific imagination and ethical sensibility.