How does online mourning differ from offline mourning? Throughout history, demographic, social and technological changes have altered mourners' social relationships with both the living and the dead, and hence their experiences of grief. Online technologies comprise the latest chapter in this story; earlier chapters include family/community mourning (preindustrial), private mourning (twentieth century) and public mourning (turn of the millennium). Pervasive social media in which users generate their own content have significantly shifted mourners' social interactions and the norms that govern them, partly in new directions (such as enfranchising previously stigmatised griefs; more potential for conflict between mourners and others) but partly returning to something more like the relationships of the preindustrial village (such as everyday awareness of mortality, greater use of religious imagery, more potential for conflict among mourners). Online, mourners can experience both greater freedom to be themselves and increased social pressure to conform to group norms as to who should be mourned and how.Online memorial culture is both a form of online culture, and a form of mourning and memorialising. This article examines it as the latter, sketching a brief history of mourning in order to show how online mourning both differs from, and does not differ from, offline mourning. Specifically, I will show how demographic, social and technological changes in recent centuries have changed mourners' social relationships with both the living and the dead, and hence their experiences of grief; online technologies comprise the latest chapter in this story. The first (1990s) generation of specialised online groups and virtual cemeteries changed surprisingly little, but from the mid-2000s social media's user generated content, together with its mobile technology-enabled pervasiveness, has been as significant as urbanisation and industrialisation in changing mourners' social relationships, not least in partially reverting to pre-industrial modes of mourning.