The way in which the bilingual’s two languages can co-exist and interact with each other is crucial for the study of language coactivation. This question has been tackled from the perspective of experimental psycholinguistics and that of language contact which can be brought together in the light of different, yet concomitant evidence related to multiple interactions between words from the two languages. Most of these interactions can be accounted for in terms of common and/or parallel morphological representations between the two languages. The two masked priming experiments using cross-script materials reported in this chapter corroborate and extend this hypothesis by showing that different ‘levels’ of morphological and/or etymological relatedness underlie different priming effects. The morphological priming pattern reflects an organisation of the lexicon based on ‘cross-language derivational families’, whereby morphologically complex L1 words automatically activate their base word in L2. Evidence that the opposite is not true suggests the existence of a looser link between L2 words and representations at the semantic-conceptual level, while still being compatible with evidence that translation primes induce significant effects in both L2-to-L1 and L1-to-L2 directions. Evidence from language contact supports the idea that the two languages do not behave in a strictly symmetric way. The more tenuous link between L2 vocabulary and a morphological/conceptual level is mirrored by the morphological integration of loan words into a matrix language, as a significant, preliminary step in the direction of a full conceptual integration. Further data from morphological integration in accordance with the cross-language priming data point to a view of the bilingual lexicon as a unified lexico-semantic architecture.