In this chapter, we explore the communication modes and tactics used by extremists across the ideological spectrum to spread their narratives on social media. We argue that a growing body of evidence suggests that extremist movements across the political spectrum make use of similar communication modes and tactics on social media to reach their objectives. Drawing on specific case studies and examples from extreme-right, conspiracy myth and Islamist extremist campaigns, this chapter highlights how groups and networks adapt to changing circumstances and external pressure by making different strategic choices about whether to use overt or covert, centralized or crowdsourced, influencer-based or network-based and aggressive or optics-focused communication modes. On a tactical level, our case studies provide insights into approaches chosen by extremist movements to radicalize sympathizers, influence mainstream audiences and intimidate political opponents. Throughout these case studies, it becomes clear that extremists are engaged in collective learning in relation to their communication modes and the use of new technologies, with approaches and instructional materials being shared and inspiring extremists across borders.