This Element endeavors to enrich and broaden Southeast Asian research by exploring the intricate interplay between social media and politics. Employing an interdisciplinary approach and grounded in extensive longitudinal research, the study uncovers nuanced political implications, highlighting the platform's dual role in both fostering grassroots activism and enabling autocratic practices of algorithmic politics, notably in electoral politics. It underscores social media's alignment with communicative capitalism, where algorithmic marketing culture overshadows public discourse, and perpetuates affective binary mobilization that benefits both progressive and regressive grassroots activism. It can facilitate oppositional forces but is susceptible to authoritarian capture. The rise of algorithmic politics also exacerbates polarization through algorithmic enclaves and escalates disinformation, furthering autocraticizing trends. Beyond Southeast Asia, the Element provides analytical and conceptual frameworks to comprehend the mutual algorithmic/political dynamics amidst the contestation between progressive forces and the autocratic shaping of technological platforms.