Massively multiplayer online games (MMOGs) are perceived to afford informal, contextualized L2 interaction. While earlier CALL research examined MMOGs as a tool for interaction and negotiation, more recent research is moving towards a game-as-ecology view, showing that L2 learning in MMOGs is a complex, interconnected, and dynamic process that is highly contingent on context. This chapter presents an ethnographic study of informal ESL learning mediated by multiplayer gameplay. Drawing on data from questionnaires, interviews, gaming sessions, and gaming journals, the author argues that L2 learners, when playing MMOGs at their own discretion, engage with those game discourses that align with their preferences of gameplay and goals of language learning. The study presented here adds to the growing evidence that affordances of MMOGs must be understood in relation to the learner's history, ability, and preference within the social context of gameplay. These components are interconnected and change dynamically in a coherent learning-gaming ecology.