The rapid development of information and communication technologies (ICTs) is influencing the way we learn. 3D multi-user virtual environments (3D MUVEs) are emerging technology that is increasingly used in computer assisted language learning (CALL). Virtual environments are immersive, virtual worlds that could enhance second language learning (SLL). However, due to the novelty of the medium, the field lacks of a complete, systematic literature review that can support or reject the argument that '3D MUVE can enhance SLL'. The aim of this paper is to map this emerging research field. For this purpose, a published method for conducting systematic literature reviews was employed. Using this method, we identified 128 relevant papers. From these, we selected 32 that included case study results and employed general purpose virtual worlds (e.g., Second Life) rather than games (e.g., Warcraft). The results suggest there is evidence of improvement in learning outcomes, communication skills and motivation. In addition, this paper sheds light on areas requiring further research, such as the instructor's role in a 3D MUVE.