Philosophising, as Spinoza conceives it, is the project of learning to live joyfully. Yet this is also a matter of learning to live together, and the surest manifestation of philosophical insight is the capacity to sustain a harmonious way of life. Here, Susan James defends this overall interpretation of Spinoza's philosophy and explores its bearing on contemporary philosophical debates around issues such as religious toleration, putting our knowledge to work, and the environmental crisis. Part I focuses on Spinoza's epistemology. Philosophical understanding empowers us by giving us access to truths about ourselves and the world, and by motivating us to act on them. It gives us reasons for living together and enhances our ability to live co-operatively. Part II takes up Spinoza's claim that, to cultivate this kind of understanding, we need to live together in political communities. It explores his analysis of how states can develop a co-operative ethos. Finally, living joyfully compels us to look beyond the state to our relationship with the rest of nature. James concludes with discussions of some of the virtues this requires.