This article provides the first theoretical treatment of the ontologies and epistemologies of digital heritage research at the time of the interconnected and social web, based on extensive empirical and analytical investigation. We draw on observations and concepts developed while conducting the first study of public experiences of the past that utilised big data – over 1.4 million Facebook posts, comments and replies – to revisit or generate new theory from the ground up. We expect that this will help scholars from a range of fields in the humanities, social and computing sciences who are interested in undertaking digital heritage research to understand the deeper implications of their work, the complexities and limitations of the knowledge they create, and its value in exposing the processes via which heritage is made and assessed.