This thesis attempts to describe lexical relationships between sentences in text and between utterances in discourse in the light of pragmatics and psycholinguistics. It was inspired by Halliday and Hasan's pioneering effort to describe relationships of cohesion in text but it goes beyond their taxonomy of lexical cohesion to include pragmatic aspects that can serve the purposes of PL reading research Thus, the motivation of the present research is twofold: i To describe lexical cohesion as a "competence" phenomenon by determining the factors contributing to its achievement in text. ii To provide an account of lexical cohesion as a "performance" phenomenon by investigating the factors affecting its interpretation in FL reading comprehension. The articulation of the thesis reflects these two issues: the first Chapter is a linguistic account of lexical cohesion in English. It lays out the basis on which cohesion and lexical cohesion should be distinguished from coherence and lexical coherence, and reviews the literature which has treated these phenomena in relation to the theoretical framework adopted for the present study. Thus, two main categories are proposed for the analysis of lexical cohesion as a competence and performance phenomenon: lexicosemantic cohesion which accounts for the connectedness of "text" and lexicopragmatic coherence which is a feature of the connectedness of "discourse". The Chapter also provides detailed analysis of the lexical devices of cohesion and coherence in the light of theories of semantics and pragmatics. Chapter Two examines the involvement of the cognitive factor in the analysis of lexical cohesion. It deals with the concept of "background" or "schematic" knowledge viewed as an essential component of the reading process and investigates the role of top-down and bottom-up processes in the making of linguistic and pragmatic inferences specifically when unknown vocabulary items are encountered in reading (comprehension). In Chapter Three an experimental investigation of the linguistic and non- linguistic features of the interpretation of lexical cohesion in reading comprehension is proposed. It seeks to inquire into the processing of lexicoreferential, lexicosubstitutional and "conjunctive" relationships of cohesion and coherence by non-native readers of English and attempts to answer the following three research questions: iii 1 How do FL learners 1 linguistic cohesion inferencing unknown 2 How does the use of coherence vary as a 3 How does the use of coherence vary as a ztilise lexical resources or links of and pragmatic coherence when meaning while reading? lexical resources of cohesion and function of FL proficiency? lexical resources of cohesion and function of language background? Four experiments were designed to that effect and nullhypotheses were formulated to test the performance of subjects on a cloze test in four types of independent variables. The findings which reveal that the use of lexical resources of cohesion and coherence were a function of language proficiency rather than language background, bear some pedagogical and other implications which are discussed in the final Chapter.