Originally devised as an applied enterprise, Contrastive Linguistics (CL) then aimed at producing more efficient second language teaching methods and tools, (Fries 1945, Lado 1957, Fisiak 1981). Initially based on a behaviorist view of language acquisition, CL lacked solid foundations in learning psychology. Its early attempts were criticized for overemphasizing the role of interference as a source of errors, and thereby ignoring various parameters (mediated/natural acquisition, L2/3 acquisition, etc.). This research aims at showing that, in its current form, CL should rather be perceived as a ‘double’ interface: between theory and application and between various linguistic approaches (Errors Analysis – EA –, Translation Study and Language Typology). Firstly, it shows how empirical problems, hindering the original contrastive enterprise, led to the emergence of EA, which primarily focuses on what problems actually occur in language acquisition and uses findings to solve them. The question is whether one can deal with learners’ errors in ignoring their L1. Not long ago, some pedagogical approaches had decreed a total ban of L1 in L2/3 teaching. Recently, research re-established L1-L2 transfer as a major factor in L2/3 acquisition, (Selinker 1992, James 1998). As Granger (2003) puts it, the globalization of society has led to an increased awareness of the importance of interlingual/intercultural communication. Based on the interconnections between CL/EA and their distinctive limits, we advocate that, despite their apparent opposition, they are rather complementary fields, with converging points and common goals to L2/3 acquisition. For instance: -As Krzeszowski (1990: 64) shows, learner’s L1 is important to understand an error like *these his children (ill-formed in English) vs te jego dzieci, (well-formed in Polish). -Similarly, how can we explain the errors in the following sentence of a French student, in discarding his L1? ... some people (er) conduce conduces us to a an hospital and (em) (er) the moral (er) in (er) that history is that... [LONGDALE_LEARNER-CORPUS]. -For advanced learners, many studies show how CL gives them a huge advantage from a direct comparison of their L1 with L2/3. This is a crucial point in multilingual contexts such as in Reunion Island or areas where English is not an L2, but L3 or sometimes L4, (König and Gast 2009). Finally, the study also examines how corpus-based approach emerges as a common empirical ground to CL and EA. Large corpora have given CL a much more solid empirical basis than the original intuition-based approach. Some references Fries, C. C. 1945. Teaching and Learning English as a Second Language. Ann Arbor: University of Michigan Press. Granger, S. 2003. “The corpus approach: A common way forward for contrastive linguistics and translation studies?” In Granger et al., Corpus-based Approaches to Contrastive Linguistics and Translation Studies. Amsterdam/Atlanta: Rodopi, pp. 17–29. James, C. 1998. Errors in Language Learning and Use: Exploring error analysis. London: Longman. König, E. & Gast V. 2009. Understanding English-German Contrasts. 2nd ed. Berlin: Erich Schmidt Verlag. Krzeszowski, T. P. 1990. Contrasting Languages: The Scope of Contrastive Linguistics. Berlin: Mouton de Gruyter. Lado, R. 1957. Linguistics across Cultures. Ann Arbor: University of Michigan Press.