In the history of the Western world, few men have had a greater impact on humanity's learning than Thomas Aquinas. Having written dozens of different publications, including his famous Summa Theologiæ, on topics ranging from angels to philosophy; from law to theology, Thomas has secured a permanent place in academic history. Although he never wrote directly on the topic, Thomas also influenced the field of ethics, especially through his “Treatise on Happiness,” found within his Summa. In these treatises, Thomas describes in detail the nature of happiness and how happiness is achieved. In the field of ethics, this work is important because it embraces the Aristotelian ideal of how a happy person is just, or ethical. Thomas embraces Aristotle's ideas throughout his work and goes on to comment on and Christianize many of Aristotle's original ideas, including how happiness affects our senses and faculties. One of the most interesting developments in the “Treatises on Happiness” is the combination of Aristotelian concepts of happiness, found in the Nicomachean Ethics, and the Augustinian idea that happiness is not available in this life. In this essay, I will highlight the importance of Aquinas's "Treatise on Happiness" and recognize its importance in the context of the philosophers who preceded Aquinas, namely Aristotle. Before proceeding, it is important to recognize how Thomas defines happiness and how this contrasts with those philosophers who preceded him. Aristotle wrote extensively about happiness in his Nicomachean Ethics and argued that: “happiness is an exercise of the vital faculties in accord with perfect virtue or excellence.” By this Aristotle means that happiness is the use of man's reason, which... will be used halfway through the paper... to practically move towards happiness. Works Cited Aristotle. Nicomachean Ethics, translated by F.H. Peters, MA 5th ed. London: Kegan, Paul, Trench, Truebner & Co., 1893. Accessed 22 November 2014.http://oll.libertyfund.org/title/903.Challoner, Richard., ed. The Douay-Rheims Bible. Douay: Kellah, 1750. Accessed November 22, 2014. http://www.drbo.org/DeYoung, Rebecca Konyndyk, Colleen McCluskey, and Christian Van Dyke. Aquinas' ethics. Notre Dame: University of Notre Dame Press, 2009.Plato. The Republic, translated by B. Jowett, MA 3rd ed. Oxford: Clarendon Press, 1888. Accessed 22 November 2014. http://oll.libertyfund.org/title/598.Thomas. Summa Theologiæ, translated by the fathers of the English Dominican province. New York: Benziger Bros., 1947. Accessed November 22, 2014. http://dhspriory.org/thomas/summa/index.html.