In an era of fostering multilingualism worldwide, using more than one language daily for the minor ethnic communities is a common practice. It is not quite clear, however, whether bilingual individuals who use more than one language daily, but to different extents and with different proficiencies (i.e. balanced and unbalanced bilinguals) would be more successful when acquiring English as a third language (L3) than learners acquiring English as a second language (L2) with no active use of other foreign languages. The main purpose of the proposed project is to address this gap by testing the effects of an input-based instructional intervention (Processing Instruction) and to find out whether its effects, well established for second language acquisition with learners of various first language backgrounds and across different language combinations, will hold equally true for third language acquirers of English. Reaction times and accuracy-data will be collected within a pre-/posttest design in two multilingual countries (Austria and Macedonia).