What happens to our accounts, data, and digital identities after we die? Over 550,000 US Facebook users will die in 2015, but their deaths will not necessarily result in the elimination of their accounts or their place inside a network of friends. This leaves friends and families with both the opportunity and challenge of incorporating digital identities into their practices of grief and mourning. Meanwhile, post-mortem digital identities require designers and administrators to address the ongoing use and maintenance of post-mortem data. In this dissertation, I present findings from mixed-methods research on digital afterlives. I identify how people interact with profiles after the account holder’s death, describe “post-mortem social networking" practices, articulate the multiple and conflicting needs of survivors, and present design research addressing the management of post-mortem digital identities. Framed within the larger scholarship on digital identity, I argue that digital identities are the byproduct of social performances that have been delegated into a technical system such that the system can re-present these performances. Through the study of post-mortem digital identities, I demonstrate ways that digital identities stand in as the deceased in both the social practices of friends and family and the technical functionality of social network sites.