Aristotle's concept of lexis has been discussed by numerous scholars, yet no comprehensive account of lexis has been produced so far. To fill this gap in scholarship, this thesis offers a systematic analysis of Aristotle's concept of lexis by dividing it into three levels, which allow a step-by-step approach to understanding this multi-layered concept. By considering Plato's and Isocrates' thoughts on lexis, Chapter 1 outlines the intellectual context in which Aristotle's ideas on the concept of lexis developed. Chapters 2-5 focus on the three levels of lexis and Chapter 6 brings a concluding discussion of metaphor. In Chapter 2 the linguistic elements treated under the notion of lexis and Aristotle's theory of language are delineated. These not only present Aristotle's thoughts on language as an abstract system, but they also form the most fundamental level upon which the remainder of Aristotle's thoughts on the concept of lexis are based. Chapter 3 explores Aristotle's remarks regarding individuals' use of linguistic elements as determined by sociolinguistic factors. Aristotle's occasional statements about language usage within the concept of lexis provide valuable pieces of evidence for studies in sociolinguistics and for his ideas on lexis on its third level as discussed in Chapters 4 and 5. In Chapter 4 the intra-textual aspect of Aristotle's remarks on lexis as a means for the creation of different kinds of poetry and rhetoric, i.e. lexis as technē, is examined. In Chapter 5 extra-textual factors are considered and are followed by a discussion of the purpose and function of lexis on its third level. Chapter 6 concludes the discussion of lexis by focusing on metaphor, the linguistic and stylistic element par excellence treated under the notion of lexis, which further highlights the benefits of a three-level approach to Aristotle's concept of lexis.