In his main work, The World as Will and Representation, first published in 1819, Schopenhauer presents his philosophy in its entirety and systematically. In the first two of the four "books" of the work, which are included in the first volume of the Greek edition, he deals firstly with the object, the composition, and the limits of human knowledge (Book A), and then with the essence of things, the substance of reality (Book B). Human knowledge is determined by the a priori forms of the subject's cognitive mechanism and is conducted firstly at the level of perception and then at that of abstract knowledge. Access to the essence of things is provided by our immediate inner experience of will, which constitutes the metaphysical substance of reality.

The World as Will and Representation is undoubtedly included among the great classic works of European philosophy, with a great influence in all areas of human thought. It incorporates a large part of the earlier philosophical tradition and is itself a very important source of modern philosophy, both directly and indirectly.