This talk will give an overview of the EPSRC/ESRC Foresight project 'Developing Theory for Evolving Socio-Technical Systems' (TESS). The project is based on Robin Dunbar's Social Brain Theory that explains the evolutionary constraints on human relationships and social organisation. With the spread of Social Networking Sites such as Facebook and MySpace, will we be able avoid those constraints to keep up with more friends and be more social, or is the downside, invasion of privacy, stalking, and a less social world ? The TESS project is researching these issues by studying social networks and work-related groups. I will describe current research on social networking sites and how this fits into the wider picture of social mediating technologies such as Twitter, Wikipedia, etc. Investigating the questions- does technology really change the way we behave in our social life, how do we adapt and use these technologies, and what impact might technology have a social capital?