Abstract: Social movements are increasingly using social media, and Twitter in particular, to reach existing and new publics and advance their mission. While historically movements had to rely on traditional media to connect with such publics, via social media any user can share content, helping to connect the key players within the movement to new publics. The quality of highly shared content, however, has been under scrutiny. The #BlackLivesMatter movement, one of the most prolific and popular hashtag movements on twitter, is examined as a case study, in order to determine the role of content importance and emotion on the virality of the movement. Four aspects of importance were examined – Policy or Action, Group, Social Actor and Politics– as well as direction of sentiment. Findings suggest important tweets were more likely to be retweeted, where tweets associated with policy or action showing the strongest relationship with retweeting. Tweets with expressed emotion were more likely to be retweeted than neutral tweets. When tweets contained important content related to Policy or Action or a Group as well as sentiment, these tweets were most likely to be retweeted, revealing a method for social movements to increase effectiveness. Theoretical and practical implications are discussed.