For multinational corporations, the need for efficiency and control has motivated the choice for a corporate language. However, increasing internationalisation has forced corporations to rethink their language policies to cater to the changing demands of the multicultural and multilingual workplace. This paper explores two related issues. First, it addresses the influence of mode of communication (English as a Lingua Franca [ELF] vs. L1-L2 interactions) on task efficiency. Second, it investigates the use of communication strategies in the different types of interactions (ELF vs. L1-L2). In a within-subject experimental design, the present study explores the effectiveness of language use in dyadic, computer-mediated communication between non-native speakers of English (ELF) and native and non-native speakers of German and Dutch (L1-L2). In three consecutive chat sessions, 60 participants performed a problemsolving task in English, German or Dutch. Findings indicate that in L1-L2 interactions, the participants were more effective in realising communicative goals than in ELF interactions, and that participants made use of different communication strategies in L1-L2 interactions than in ELF interactions. Consequently, international organisations which implement a corporate language may benefit from condoning multilingual practices on the work floor.computer-mediated communication (CMC) activities for (inter)national interactions (e.g. Tworoger et al. 2013) on a daily basis (e.g. Twitter, Facebook, MSN), the purpose of this study was to investigate the effectiveness of language choice in CMC interactions.Business communication research has demonstrated that despite a corporate (monolingual) language policy, communication in companies is often multilingual, with several languages coexisting alongside the corporate language in the workplace (Angouri 2013;Kingsley 2013;Lüdi, Höchle, and Yanaprasart 2010;MacKenzie 2012).Although the use of a corporate lingua franca may facilitate global communication in multilingual settings, it may also present linguistic, cultural and organisational challenges for those who are non-native speakers of the corporate language. For instance, Welch, Welch, and Piekkari (2005) showed that, although knowledge transfer and information processes are considered of paramount importance to internationally operating companies, language often remains a 'forgotten factor' in many multinational organisations in that organisations often overlook the (immaterial) costs and consequences of the implementation of a single corporate language. The use of a corporate language may exclude non-native staff lacking adequate proficiency from communication processes, and, conversely, put considerable power into the hands of those individuals or units that do possess the required language skills (Welch et al. 2005). In her analysis of international business meetings, Rogerson-Revell (2008) showed that the use of English as a Lingua Franca (ELF) may lead to feelings of frustration in meetings and that a considerable...