Social media platforms have continually reshaped their architecture, integrating mobile devices and different affordances to offer new opportunities to expand personal networks, interact with others, and share information. This has led to evolving boundaries between public and private. While receiving benefits from a variety of uses, users also encounter different risks given that rich repositories of personal data are stored. Navigating "socially mediated publicness" has become an ever-changing process that affects how users define the boundary of public and private and influences users' behaviors and social interaction. Social media also serves as a channel that reframes media and news content and as a platform that facilitates exchange between private and public discourse. This special issue features six articles addressing the changing dynamic of publicness on social media and its relationship to the contemporary communication ecology. It is intended to facilitate understanding of the blurry boundary between public and private and its impact in various realms.