Within a European project on Networked Interaction in Foreign Language Acquisition and Research (NIFLAR), "Second Life" was used as a 3D virtual world in which language students can communicate synchronously with native speakers in the target language, while undertaking action together. For this context, a set of design principles for interaction tasks was developed aiming at maximizing authentic social interaction and intercultural awareness, while exploiting the specific affordances of the virtual environment being used. These design principles were applied and tested in a case study in which two foreign language learners of Spanish and two pre-service teachers carried out four interaction tasks in the virtual world of "Second Life". In this article we first present and discuss the framework for task development and assessment. We then show the results of the case study conducted in "Second Life" which aimed at: (1) applying and assessing the design principles for task elaboration, (2) analyzing the kind of interaction the tasks elicited in the virtual world, (3) exploring whether the specific affordances of the virtual environment were adequately used for enhancing interaction, and (4) studying whether and how the condition anonymity versus familiarity may play a role in modeling virtual interaction. (Contains 1 note and 4 tables.)