Almost 50% of the EU citizens are bilinguals, and Europeans acknowledgement of the need of knowing another language is clearly growing. However, second language (L2) learners L2 production has been shown to be affected by the first languages properties. For example, traces of some L1 phonological or syntactic properties are shown in L2 learners production.However, precise characterization of this phenomenon is still lacking and it is unfortunately still poorly understood. Consequently, this project aims at studying in-depth the way L1 syntax affects bilinguals L2 sentence processing. Specifically, we will focus on the way grammatical agreement is computed in bilinguals L2 sentence production. Agreement encoding processes (e.g., subject-verb number agreement) have been largely studied in language production through the elicitation of agreement errors in sentence completion tasks.For example, participants are presented with a sentence preamble they are asked to complete in such a way as to produce a grammatical sentence (the key to the cabinetsis/*are red). Several factors is shown to affect agreement encoding (e.g., semantic and morphophonological factors). Moreover, cross-linguistic differences have been found in the way these factors affect agreement processing. Therefore, this project will put special emphasis on the role syntactic similarity between L1 and L2 plays in bilinguals L2 agreement encoding. The sentence completion task will be used to study L1 and L2 agreement encoding in different languages (English, Spanish and Basque).First, in order to find both cross-linguistic differences and similarities, the main factors affecting agreement encoding in native speakers of these languages will be characterized. Then, different types of bilingual speakers (e.g. English-Spanish, Spanish-Basque) L2 agreement encoding will be tested. In such a way, to what extent L1 syntactic properties modulate the capacity of L2 production will be determined.