Self-presentation refers to how people express themselves - through their physical appearances, behaviors, and attitudes - to shape how other people perceive them. Self-presentation has been one of the most important motivations for people to use social media since its earliest days. As social media platforms have become more popular, people have increasingly incorporated multiple platforms into their daily lives, presenting themselves in front of different audiences across these platforms and taking advantage of different platform features and affordances to help them shape their self-presentation.

The vast majority of social media research on self-presentation focuses on single platforms. In addition, while posters and audiences are both important parties in the process of self-presentation, most research emphasizes posters' voices in how they build up their online images while ignoring audiences' voices in how they perceive and respond to posters' self-presentation. In this dissertation, I explore differences in individuals' social media self-presentation across three important dimensions in their social media space: time, account, and platform; and how their audiences perceive the differences in their self-presentation. This dissertation research consists of four studies with a combination of qualitative (e.g., interviews) and quantitative (e.g., survey) research methods. The results unpack how people's self-presentation is shaped and supported by affordances, features, and sociotechnical factors like norms within their personal social media ecosystems and how the relationship between posters and audiences is constantly fine-tuned in the process of self-presentation.