This document reviews the pedagogical foundations of learning in virtual worlds. It discusses the research problem of whether virtual worlds are designed for learning based on educational research and theory. It then describes the literature search conducted on this topic, identifying over 260 articles from various databases published between 2000 and 2010. The document notes that virtual world literature comes from many sources and can be ambiguous. It proposes using an exploratory case study method to bring rigor to reviewing this multivocal literature. Coding criteria are presented for determining if a virtual world is grounded in pedagogy based on four conditions: a theoretical framework, consistency with research methods, generalizability, and iterative validation. An example virtual world project is then analyzed against these criteria.