Abstract : The research for this thesis explored and compared the degree of lexical complexity demonstrated in the written discourse of EAP and ESP learners studying at university in the Kingdom of Bahrain. A total of nine thousand five hundred words were analyzed from learners across each context and varying methods of quantitative analysis were conducted to measure the lexical density, diversity, and sophistication of the discourse produced. The results were then further analyzed using the SPSS software, which demonstrated that the results were indeed significant, with EAP learners attaining slightly higher lexical density in comparison to the ESP learners. When lexical sophistication was considered, the TAALES 2.0 program was utilized to compare the written discourse of the learners in contrast to the British National Corpus, the Brown Verbal Frequency, as well as N-gram indices. Further qualitative analysis was also conducted to explore the perspectives of learners from both EAP and ESP contexts towards lexical complexity. Keywords: EAP, ESP, lexical density, lexical diversity, lexical sophistication