What How do present-day social networks differ from those in the past, and how have these structures changed over centuries? The key to these important questions lies with archaeological and historical network research, offering the material and textual sources that document interactions between past individuals. But answering such questions is currently hampered by a number of challenges: past social network data are rarely being made open access and a methodological pipeline for comparative studies of centuries-long change in past social networks is missing. The Past Social Networks Project aims to address these challenges. Why Network research in archaeology and history has the potential to enhance our understanding of long-term changes in human interpersonal networks. To allow this young discipline to achieve this potential requires the ability to quantitatively compare social network structures from many different times and places. This can be enabled by pursuing a practice of the open deposition and documentation of past social network data and their related uncertainties, allowing replication of previously published observations of network structures, and the assessment of the impact of missing and uncertain information. How The Past Social Networks Project will establish the first open online repository to stimulate the practice of open publication, documentation and re-use of past social network data. Substantive case studies of social networks in the Roman Empire will inform the creation of this repository and of formal methods for comparing the structures of past social networks. It will organise networking activities to more firmly establish long-term change in past social networks on the network science research agenda. SSR A higher availability of past interpersonal network data will enable a future better understanding of how information or viruses spread between individuals in the past, and to explore the extent to which such flows differ in the present. Such comparisons can help understand how major changes in communication and interaction technology have reshaped interpersonal interactions.