The present thesis is an examination of eight Greek-speaking aphasic speakers with non-fluent speech following a focal lesion or a haemorrhagic episode in the left hemisphere. Our study re-examines the notoriously problematic competence-performance issue from a novel perspective that focuses on the agrammatic processing of the interfaces. Thus, the explanatory framework we adopt considers the language faculty to incorporate interfaces between distinct components of the grammar, so that agrammatic deficit may not be strictly localized on the subcomponents of the syntax, the morphology, or the lexicon.A series of both on-line and off-line experiments was run across both the comprehension and the production modality, with the aim of circumventing processing to linguistic structures conditioned at the discourse-syntax and the lexicon-syntax interface. More specifically, the aphasic group (along with the fifteen language-unimpaired control subjects matched with the aphasic patients along age and educational level) were administered two on-line tests checking the interpretation of null and overt subject pronouns in referentially ambiguous intra-and inter-sentential contexts, as well as a sentencepicture matching, an elicitation, a repetition, and a cross-modal lexical priming task checking the production and processing of reflexive, transitive and (both active and non-active) anti-causative verbs in Greek. The results of these experiments show selective difficulty (i) with the integration of discourse information regulating the interpretation of the overt subject pronoun, and (ii) with accessing lexiconfiltered information regulating the anti-causative sub-categorization of active intransitive verbs. The data also reveals the extensive use of compensatory and heuristic strategies on behalf of both the controls and especially the eight aphasic patients, primarily aiming at offsetting the computational cost under deep processing conditions. The parsing preference of subject prominence, the non-active morpheme serving as a cue to transitivity changes in verbs, and animacy heuristics were among the most popular parsing strategies found to be employed during off-line and (mainly) on-line sentence processing. We speculate on these findings in terms of both performance (vs. competence) limitations related to the Abstract xiv properties of interface-conditioned information, as well as a conceptualization of Broca's aphasia through both linguistic and cognitive/executive dysfunctions.