This paper will endeavour to present an outline of the Organic Philosophy associated with the name of Whitehead. Whitehead resembles Spinoza and Leibniz in that he is a philosopher who has tried to construct a world-outlook that will do justice to science and to the other aspects of life and knowledge. Moreover, just as in his day Leibniz was an eminent mathematician and scientist, so Whitehead in our day enjoys the same distinction. But Whitehead's philosophy differs both from that of Spinoza and from that of Leibniz. Spinoza based his philosophy upon the monistic substance, of which the actual events in the world are the inferior modes. Whitehead bases his philosophy upon the actual events themselves and derives the solidarity of the world as a whole from their mutual interplay. Thus the organic philosophy is pluralistic in contrast with Spinoza's monism. In comparing Whitehead's philosophy with that of Leibniz, we find that they agree in both being pluralistic, but they differ in the emphasis placed upon the notion of mentality. Leibniz's monads are best conceived as generalizations of the notion of mentality, and the conception of physical bodies only enters into his philosophy subordinately and derivatively. Whitehead, however, in his philosophy of organism endeavours to hold the balance between the physical and mental more evenly, and thus does justice to both aspects of reality.