A particular challenge in the area of social media analysis is how to nd communities within a larger network of social interactions.
Here a community may be a group of microblogging users who post content on a coherent topic, or who are associated with a speci c event or news story. Twitter provides the ability to curate users into lists, corresponding to meaningful topics or themes. Here we describe an approach for crowdsourcing the list building e orts of many di erent Twitter users, in order to identify topical communities. This approach involves the use of ensemble community nding to produce stable groupings of user lists, and by extension, individual Twitter users. We examine this approach in the context of a case study surrounding the detection of communities on Twitter relating to the London 2012 Olympics."