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 about issues such as religious toleration, how we use our knowledge, and the environmental emergency. Part I focuses on Spinoza's epistemology. Philosophical understanding empowers us by giving us access to truths about the world and ourselves, and by motivating us to act on them. It gives us reasons for living together and enhances our ability to cooperate. Part II takes up Spinoza's claim that, to cultivate this kind of understanding, we need to live 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. The concluding section of this book focuses on some of the overarching virtues this requires.