Despite the growth and commercial potential of virtual worlds, relatively little is known about what drives users' motivations to engage in virtual worlds. This paper proposes and empirically tests a conceptual model aimed at filling this research gap. Given the multipurpose nature of virtual words the model integrates extrinsic and intrinsic motivation as behavioral determinants. By making use of the literature on information system value and motivation theory four important system-specific virtual world characteristics (economic value, ease of use, escapism, visual attractiveness) are added as motivational drivers. Using structural equation modeling on a sample of 846 users of the virtual world Second Life the hypotheses were tested. The results support the model; they confirm the role of extrinsic and intrinsic motivation as behavioral determinants and show how and to what extent the four system-specific elements function as motivational basis. Implications for research and practice are discussed. © 2011 Elsevier Ltd. All rights reserved.