This chapter will cover some of the key theoretical and practice issues associated with how social media impact on group and individual behaviour. The chapter will also address practical issues of relevance to professionals considering using social media as part of their efforts to promote mental health. In the opening section, we set out an introduction to relevant behavioural theory and its implications for social media practice and how it can be used to promote positive engagement with social media. The chapter will also examine how social media can be harnessed to promote mental health and provide guidance about the design and use of social media in the field of mental health promotion. It will provide practitioners with understanding about how social media can have negative influence on both personal and group behaviour and how this can be minimized. The chapter will conclude with practical examples about how to utilize social media in mental health promotion and guidance that can be given to clients about how best to use social media as part of their own mental health promotion. The chapter will be illustrated with case studies and examples from a variety of countries.