Social networking services, such as Facebook, are important channels of communication both for monolingual users and for those having various degrees of proficiency in L2, with the latter deploying expression both from L1 and L2. It can, therefore, be presumed that communication on FB plays a role in practicing the use of L2. One of the phenomena that can be examined in relation to that are various forms of code-switching. There is animmense research gap related to Polish-English code-switching appearing on this SNS. To obtain a full picture of the issue, the paper identifies and discusses types, strategies, and functions of Polish-English code-switches found in posts and comments published by Poles on Facebook in 2014–2019. It also indicates possible applications of FB tools and materials including CS in foreign language teaching and learning and shows how Facebook enables “social learning” (Mallia, 2013). The research is based on a corpus constructed by the author of this article. An integrated approach with both qualitative and quantitative methods of analysis is used in the paper. Three main CS types (intrasentential, intersentential, and tag-switching) and strategies (alternation, insertion, and congruent lexicalisation) have been attested in the material. The code-switches mostly indicate in-group membership but also, for example, introduce humor, quotes, and signal a lack of L1 equivalents. The study points out that there are certain relations between the types, strategies and functions. The resultsof the research are collated with the recent studies on Polish-English and Indonesian-English CS on Facebook.

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