This dissertation seeks to investigate the use of apophatic discourses as epistemological tools in situations where language seems to reach its limits, with special emphasis on the mystical-religious context. How to talk about God, understand the ultimate nature of reality or conceive what was before the origin of the universe? Mystics, religious people and poets, as well as philosophers, physicists and cosmologists have been dealing with issues like these for a long time. Throughout history, catapathic (affirmative) language has seemed, to many of them, to be unable to answer these questions; and, perceiving it as insufficient, the great religions, in particular, adopted a type of discourse that came to be known as apophatic discourse, or via negativa. In order to examine some techniques of negation employed by mystics and contemplatives in the face of the difficulties they encounter in talking about the ineffable, this dissertation contrasts the works of two central figures in their respective religious traditions: Mystical Theology, by the Christian Dionysius, the Areopagite, and The Fundamental Wisdom of the Middle Way, by the Buddhist Nagarjuna - texts known for taking denial to the extreme. Through this comparison, and relying mainly on the commentators Denys Turner, Eric Perl and Giuseppe Ferraro, this study points out and discusses significant differences between the negative languages used in the two works. Finally, it discusses, briefly, how these discourses relate to contemporary counterparts and parallels, such as the philosophical thought of Jacques Derrida and the discoveries of modern physics in the early 20th century.