In the field of second language acquisition (SLA), the study abroad context (SA) has gained attention as a site that offers the potential of significant second language (L2) development due to high amounts of input and interaction opportunities compared to at home foreign language (AH) and domestic immersion (IM) contexts (Pérez-Vidal, 2014). In previous research, the SA context has been a country where the L2 is the local language (e.g., English in the United Kingdom). However, with the increase of student mobility programs across Europe, such as ERASMUS, and the status of English as an International Language, another study abroad context is available, one where students can take English-medium classes and use English as a lingua franca in a country where English is not the local language (e.g., Germany, Poland, Spain). In the current study, this new context is operationalized as English as a lingua franca study abroad (ELFSA), the effects of which have received very little attention in SLA to date. By providing an alternative SA context through English medium of instruction on-campus, and English as an international language through off-campus interactions, this new context might bring further insights into the SA phenomenon. Motivated by this gap in the literature, the current longitudinal study aims to investigate the differentiated effects of the SA, ELFSA, and AH contexts on the linguistic development of Turkish undergraduates whose L2 is English. Given the multilingual nature of the ERASMUS context, this study also examines the contextual influences on participants’ perceptions towards multilingualism from a Perceived Positive Language Interaction (PPLI) perspective (Thompson, 2013). The participants of the study were 50 third year Turkish undergraduates, 33 of whom undertook a 16-week ERASMUS exchange semester in Spring 2016. Following a quasi-experimental mixed-methods pretest-posttest design, data were collected via a one-minute spoken and 15-minute written production test to determine linguistic complexity, accuracy, and fluency gains; an Elicited Oral Imitation Test (EIT, Ortega et al., 1999) to measure pre-departure proficiency; a monthly online Language Interaction Questionnaire to investigate the type and amount of language contact; and a dichotomous questionnaire to learn about participants’ perceptions towards multilingualism within PPLI. For triangulation purposes, qualitative data were collected via several open-ended items in the questionnaires and semi-structured interviews. The results of the quantitative and qualitative analysis indicated that the SA and ELFSA contexts were beneficial for English development on most of the measures, yet the former had certain issues for the participants pertaining to the dominant variety and features of spoken English (e.g., weak forms, connected speech, speech rate). The ELFSA was reported to be more multilingual as compared to the SA, also paving the way for seeing further Perceived Positive Language Interaction (Thompson, 2013) among the additional languages that their participants knew. The major difference between the two was described to be the ELFSA participants’ developing an ELF identity towards using English as an L2, as they tended to prioritize fluency over accuracy throughout their exchange semester. The results of the quantitative analysis indicated that the AH group had significantly more gains on written fluency than the two abroad groups. Also, time was found to be a significant factor for lexical development regardless of group differences. In terms of oral gains, main effects of time indicated that the participants as a whole group had significantly different means over time on speech rate and breakdown fluency, the inspection of which showed that the ELFSA had the highest mean differences. As for oral accuracy and lexical complexity, an interaction effect between time and context group was found to approach significance, indicating that both sojourn groups had mean gains on the former, while only the ELFSA had higher mean scores in the posttest for the latter measure. Finally, the data from the semi-structured interviews provided a holistic picture of the interplay between context and development in English. The major finding of the study, thus, indicated that the SA may not be the sole provider for intense L2 input to improve English during a semester abroad; the ELFSA appeared to be equally as beneficial as the SA in terms of linguistic development with a bonus of creating a linguistic identity of an ELF speaker for language learners. The study also provided several empirical and pedagogical implications for those interested in the stay abroad and its influences on L2 development.