This thesis investigates the relationship which both academic vocabulary and lexical bundles have to academic performance at university. While academic vocabulary is defined in terms of the University Word List (Coxhead, 2000), lexical bundles are identified as groups of four words that commonly co-occur, such as on the other hand and as a result of. A corpus of student essay writing in a single discipline, psychology, was developed over the course of a three-year undergraduate degree. To provide a benchmark against which to compare the student academic writing, a corpus of published articles in the same discipline was developed. The VocabProfile program (Cobb, 2002) was used to establish the density of academic vocabulary in the student essays. Similarly, the density of lexical bundle use was analysed by means of WordSmith Tools (Scott, 2012). The densities were then correlated against students’ academic performance as measured by their essay results. Comparisons were also made between the use of academic vocabulary and lexical bundles by first- and additional-language speakers, and by first- and third-year students. A keyness analysis enabled comparisons of academic vocabulary and bundle usage by high and low achievers. An additional aspect of this study was the comparison of densities of academic vocabulary and lexical bundles found in the IELTS writing test and in student essays, and the correlation of IELTS reading and writing test scores to students’ academic performance. The students’ vocabulary knowledge was also tested by the application of receptive and productive vocabulary tests, and the results compared to their academic performance. Results indicate that the 10 000-word level is a stronger predictor of academic performance than either the 5000-word level or academic vocabulary, and that there is a significant relationship between the density of lexical bundle use by students and their academic performance. Both vocabulary measures are therefore arguably better predictors of academic performance than the IELTS test scores. / Linguistics and Modern Languages / D. Litt. et Phil. (Linguistics)