Doctoral Thesis / Dissertation from the year 2016 in the subject Speech Science / Linguistics, grade: A, Eötvös Loránd Tudományegytem (Doctoral School of Education), course: PhD Programme in Language Pedagogy, language: English, abstract: Due to the various functions and diverse attitudes to lexical repetition in discourse, it is an aspect of cohesion which creates difficulty for raters when assessing L2 academic written discourse. Current computer-aided lexical cohesion analysis frameworks built for large-scale assessment fail to take into account where repetitions occur in text and what role their patterns play in organizing discourse. This study intends to fill this gap, by applying a sequential mixed method design, drawing on Hoeys (1991) theory-based analytical tool devised for the study of the text-organizing role of lexical repetition, and its refined version, Károlys (2002) lexical repetition model, which was found to be capable of predicting teachers perceptions of argumentative essay quality with regard to its content and structure. It first aims to test the applicability of the previous models to assessing the role of lexical repetition in the organization of other academic genres, then propose a more complex, computer aided analytical instrument that may be used to directly assess discourse cohesion through the study of lexical repetition.In order to test the applicability of Károlys model on other academic genres, two small corpora of thirty-five academic summaries and eight compare/contrast essays were collected from English major BA students at Eötvös Loránd University. The lexical repetition patterns within the corpora were analyzed manually in the case of the summaries, and partially with a concordance program in the case of the compare/contrast essays. The findings revealed that in both genres lexical repetition patterns differed in high and low-rated texts. Given that in its present form the model cannot be used on large-scale corpora, in the third stage of the research, a computer-aided model was designed for large-scale lexical repetition analysis. First, by employing the theoretical, empirical and methodological results gained from the corpora, several new analytical steps were proposed and built into a modular format. Next, in order to better align the new computer-aided analysis to its manual version, parallel processes were identified between the new analytical model and an existing sociocognitive framework. The newly proposed model may help teachers to assess discourse cohesion, or can be used as a self-study aid by visualizing the lexical net created by semantic relations among sentences in text.