Although the importance of linguistic simultaneity has long been recognized (Woolard 1998), the concept is underexamined in recent analyses of language use in globalized, digital contexts such as social media. Drawing from an analysis of everyday Facebook posts from youth in Belgrade, Serbia, the article proposes that recognizing four types of simultaneity—of linguistic features, indexical operations, effects, and scale—is key for making sense of social media utterances in political and historical context. On Facebook, Serbian youth mix languages and writing systems in complex ways, adhering to dominant ideologies of language and identity in some ways and flouting them in others. Using the Serbian case as a springboard, along with the four types of simultaneity proposed, I suggest a framework for analyzing language and identity on social media. (Serbia, indexicality, simultaneity, social media, superdiversity, bivalency, youth)*