The rise of social media platforms has changed how people interact.Mobile technologies with built-in, high-quality cameras offer new possibilities for people to document and share their everyday activities.Many consider these interaction-mediating devices to be important tools for facilitating people's social life through use of social media. The aim of this thesis is to describe what constitutes social media use in a world of smartphones with cameras, why and how social media use is meaningful as a category of activity, and to contribute with new insights on how social media skills and perceptions change as practices and platforms develop.Drawing upon data collected in 2012 and 2017, this thesis provides empirical findings from four papers. By returning to the same informants, conducting stimulated recall interviews five years apart, the data provides insights on how social media use has developed over time. In this thesis, social media use is understood as the social practices that people engage in when they plan, produce, post, and take part in social media activities.As levels of engagement in social media vary from active involvement, such as producing and interacting with content, to more passive ways of planning and monitoring social media, a revised conceptualization of