The present thesis explores the cognitive operations underlying word recognition and production of late bilingual adults in their second language (L2). Experimental psychology and electrophysiology have made a case for the activation ofthe first language (Ll) when bilingual individuals process words in L2. Evidence for cross-language activation has shaped current models of bilingual lexical processing and influenced our conception ofthe bilingual lexicon. However, previous studies have made extensive use of interlinguallexical stimuli (e.g., cognates, interlingual homographs) and/or translation equivalents to compare L1 and L2 processing in bilingual individuals. Experiments mixing stimuli from two languages create an artificial context which may differ significantly from real-life situations and bias behavioural performances toward a language-nonselective processing pattern. In the present thesis we tested bilingual participants reading, listening to, and producing words exclusively in their L2. In the first experiment series, Chinese-English bilinguals read and listened to pairs of English words, half of which shared a character repetition in their Chinese translations. Evidence of event-related potentials (ERPs)showed that Chinese translations were accessed automatically and unconsciously. In the second experiment series, the same paradigm was used except that phonological and orthographic repetitions in, Chinese translations were independently tested. Significant priming was found for phonological but not orthographic repetitions,independently of the input modality (visual or aud~ory), demonstrating that cross-language activation is mediated by phonology. In the third experiment series, speech production was studied using a covert picture naming paradigm involving rhyming decisions. Here again, L1 access was detected but it was delayed in comparison to reading and listening in L2. Moreover, cross-language activation in picture naming was asymmetric, featuring strong influences of L1 on L2, but no effect of L2 on Ll. Findings of the thesis shed new light on the dynamic nature ofhilinguallanguage processing, as well as constraints affecting cross-language activation. Implications for current models ofhilinguallexical access are discussed.