Although promising links have been established between social information processing capability (internal capability), customer co-creation (external capability), and social media agility, empirical studies have not offered sufficiently convincing evidence on the benefits of using social media. This study adopted the dynamic capability view that assesses the development of internal capability by combining information acquisition, communication, and responsiveness and examines the effect of customer co-creation on operational agility through the use of social media. Data were gathered from 231 responses to a questionnaire in a business-to-business sales context. The key contribution of this study is its examination of how social media agility is influenced by both internal and external capabilities. The results reveal these two types of capabilities to have an interactive effect on social media agility that is positively correlated with the strength of customer-firm relationships.