The Census gives us an accurate snapshot of where people live and work for one day every five years. But in a world where people are increasingly mobile across and between communities, this snapshot is starting to look out of focus. There is a large unmet demand for data showing the movement of populations and the locations in which people congregate throughout the day, week and year. This session is all about estimating mobile populations where they live, work and play. We invite papers addressing issues relating to ways of framing populations, new approaches for modelling or estimating populations or innovative uses of new or old data sources.