Virtual worlds have evolved considerably since their inception in the 1970s, beginning with simple text-based adventure games and evolving into highly immersive 3D environments such as Second Life. This entry explores the origins, development, and influential definitions of virtual worlds, emphasizing their potential in language learning. The discussion also examines avatars as digital representations of users and the combination of features that make virtual worlds unique, including real-time communication, avatar customization, and the creation of user-generated content. Despite the numerous advantages, such as enhanced language learning and increased motivation, challenges such as technical difficulties and user variables persist. Research highlights the positive impacts of virtual worlds on language learning, learner attitudes, and teacher development, underscoring their potential as valuable educational tools.