As the use of Twitter has become more commonplace throughout many nations, its role in public discussion has also increased. This has been evident in contexts ranging from political discussion through commentary on sporting and entertainment events to the coverage of natural disasters. Research into the use of Twitter in such contexts has also developed rapidly, aided by substantial advancements in quantitative and qualitative methodologies for capturing, processing, analysing, and visualising Twitter updates by large groups of users. Recent work has especially highlighted the role of the Twitter hashtag – a short keyword, prefixed with the hash symbol ‘#’ – as a means of coordinating a distributed discussion between more or less large groups of users, who do not need to be connected through existing ‘follower’ networks. For humanities and social sciences researchers interested in studying public communication through social media, this means that we face the challenge of developing new tools and methodologies for processing and analysing these potentially very large sets of data derived from Twitter. This talk presents outcomes from the Mapping Online Publics research project at Queensland University of Technology, Brisbane, Australia (http://mappingonlinepublics.net/).