Internet-based social virtual world (SVW) services have aroused extensive interest among academicians and practitioners. The success of SVW services depends heavily on customers' continuance usage, a topic not yet adequately investigated in information systems research. It is unclear to what extent, and how, the existing theories can be extended to explain the continuance usage of such services. In consideration of the distinctive features of these services, this study adapts the dedication-constraint framework of commitment and develops a model of SVW continuance, which is assessed empirically using data collected from 438 experienced users of Second Life, a typical SVW service. Results indicate that SVW customers' continuance intention is jointly determined by two mechanisms: affective commitment (being attracted to) and calculative commitment (being locked in), with the former playing a more central role. Perceived utilitarian value, hedonic value, and relational capital promote affective commitment directly and indirectly through satisfaction, while service-specific investments in personalization and relational capital increase calculative commitment. Theoretical and practical implications and future research directions are subsequently discussed.