The book begins from the insight that very few seventeenth-century philosophers have received more antithetical interpretations than Baruch de Spinoza. He has been regarded as an atheist and a rationalist, as a pantheist and a vitalist, as a Jewish critic of religion and a great thinker in the Marrano tradition. In the twentieth century, however, Spinoza was conceived as a materialist who was strikingly ahead of his time, providing Marxism with concepts of overdetermined dialectics, plural temporality and nonteleological praxis. Beginning with Althusser’s interest in the concept of immanent causality, the book reconstructs post-Marxist readings of Spinoza from Negri to Balibar, Matheron to Tosel, and Gueroult to Deleuze. It examines how these authors adapt Spinoza’s unconventional doctrines of the differentiality of being, the self-forming capacity of matter, the excess of the positive affects, and the multitude’s power of self-government. The book fundamentally revises continental philosophy’s portrayals of the relationships between matter, affect, thought, and the multitude.