A wealth of well-documented evidence in the SLA literature demonstrates that the way second language (L2) learners perceive and process foreign speech is mediated by the properties of their native language (L1). By far, the majority of inquiries have focused on the problem of acquisition of L2 segmental features by L2 learners. However, languages differ not only in their repertoire of segmental elements (vowels and consonants), but also in their repertoire and use of suprasegmental properties (these are not necessarily confined to or discretely ordered with any particular segment, but occur at some higher levels in an utterance, like syllable, word, phrase, etc.). That is why mastering L2 phonology includes not only acquisition of L2 segments, but also acquisition of L2 prosody and learning how to integrate phonetic and prosodic information in a native-like manner. By investigating the role a speaNerГs first language plays in the processing of nonnative prosodic contrasts as far as primary word stress is concerned, the present study seeks to shed more light on the mechanism underlying the formation of abstract L2 prosodic representations, and to explain how this process might be grammatically or perceptually constrained or facilitated depending on the speaNerГs L1. Specifically, the processing of contrastive word stress by speakers of three typologically different languages is examined: French, Russian, and Persian. The paper is organized as follows: Section 2 presents an overview of the theoretical and empirical literature and outlines two major challenges learners face in the acquisition and processing of word stress: the grammar learning problem and the perception problem. Section 3 provides a brief description of word stress in the three languages. Section 4 describes the tasks used in the current study, and in Section 5, the results are discussed in light of the Parameter setting theory (Chomsky, 1981; Archibald, 1993) and the current psycholinguistic approach to stress perception (Dupoux et al., 1997; 2001; 2008.). Finally, Section 6 concludes the paper.*