Introduction 'The virtual is opposed not to the real but to the actual'. (Deleuze 1994, 208). As this quote reminds us, virtual possibilities and worlds are real. As a limited actual articulation of the virtual, experiences in online virtual worlds constitute substantive components of the assemblage of subjectivity for the people about whom we write. Virtual worlds also provide possibilities for the actualization of ranges of experiences that are not possible outside forums such as Second Life. In exploring the 'realness' of virtual worlds, we advance a particular theoretical inquiry into processes of achieving social sustainability in Second Life. We give a summary of sustainable practice for web design and note the implications of the lack of discussion of sustainable practice in relation to 3D virtual worlds. We then move into virtual worlds and undertake three case studies of culture working towards being sustainable in Second Life. We take up a Deleuzian ontology as a means of thinking about sustaining cultures and valuing differenciation. After Deleuze (1994), we take differenciation to mean the material process by which something becomes different from itself. Deleuze draws a distinction between this material change and the virtual process...