xThe changes that have come about through the increased speed, ubiquity, and scale of computational systems require a reconceptualisation of how we think about and study the relationship between humans and computers. Driven by the increased production of data in interaction and the transfer of value from interaction to data, we argue that computing that fundamentally impacts human-computer relations is no longer happening only in interaction but also without and outside interaction. While recent arguments have highlighted interaction as a problematic concept for HCI — challenging what constitute users, use, the human, and the computer in interaction — we propose post-interaction computing as one means to conceptualise a fourth wave of HCI. We propose four concepts — immediacy, (un)intentionality, interaction effects, and instability — that can help us in identifying and slicing our objects of analysis in new ways that better match the challenges that HCI is now faced with.