Throughout the history of metaphysics the question: What is it? The answer has always been incomplete, unsatisfactory, or complicated, but Spinoza attempted to answer in an exceptional way by simply describing God and His essence. Based on Spinoza's view, God's qualities can be defined as attributes and modalities are simply affects of a substance. This article will provide a detailed insight into Spinoza's key ontological definition of God as the sole substance, its attributes, and their interrelations. The study goes further by exploring the main scholarly argument between Spinoza and Descartes, regarding their view of substance and its attributes. Descartes and Spinoza seem to have different perceptions regarding the existence of substance. However, both scholars have comparable perceptions of the same in some aspects. Both refer to God as the primary substance. One thing that both Spinoza and Descartes seem to generally agree on is the definition of substance. According to Spinoza, a substance is nothing more than a thing that exists in such a way that it does not depend on anything else for its survival. In the introduction to his work Ethics, Spinoza illustrates substance as "that which is conceived for itself and in itself". He elaborated this to mean that a substance does not require the sense of something else to exist, which also seems to coincide with Aristotle's interpretations of how a substance exists, which is independent of all other things. (1). The fundamental characteristic of substance, as expressed by Spinoza, is its independence. Spinoza defines God as a completely unlimited substance, or a substance "comprising an infinity of attributes", of which each of them illustrates a... middle of paper... FS 1953, Spinoza's Definition of Attribute, Philosophical Review, vol. 62, no. 4, pp. 499-513.Kline, G 1977, On Spinoza's Infinity of Attributes, London: Routledge.Melamed, Y 2012.The Constituent Elements of Spinoza's Metaphysics: Substance, Attributes and Modes (08.14.11). Johns Hopkins University. Available at: http://Philosophy.jhu.edu/wp-content/uploads/sites/7/2013/08/Spinozas-Metaphysical-BuilBlocksFinal.pdf [Accessed 5-15 December 2013]Nadler, S 2006, Ethics of Spinoza: an Introduction, Cambridge: Cambridge University Press.Pollock, F 1966, Spinoza: His Life and Thought,New York: American Scholar Publication.Rocca, MC 2008, Spinoza: The Routledge Philosopher Series, London: Routledge.Scruton, R 1999, Spinoza. London: Orion.Woolhouse, RS 1993,Descartes, Spinoza, Leibniz: the concept of substance in seventeenth-century metaphysics, London: Routledge.