Until 2016, Twitter was the online platform of choice for English-language Islamic State (IS) sympathizers. As a result of Twitter’s counter-extremism policies - including content removal - there has been a decline in activity by IS supporters. This outcome may suggest the company’s efforts have been effective, but a deeper analysis reveals a complex, nonlinear portrait of decay. Such observations show that the fight against IS in the digital sphere is far from over. In order to examine this change over time, this report collects and reviews 845,646 tweets produced by 1,782 English-language pro-IS accounts from February 15, 2016 to May 1, 2017. This study finds that Twitter’s policies hinder sympathizers on the platform, but counter-IS practitioners should not overstate the impact of these measures in the broader fight against the organization online.