Abstract: Introduction to the series Why We PostThis book is one of a series of 11 titles.Nine are monographs devoted to specific field sites (including this one) in Brazil, Chile, China, England, India, Italy, Trinidad and Turkey -they will be published in 2016 -17.The series also includes a comparative book about all our findings, published to accompany this title, and a final book which contrasts the visuals that people post on Facebook in the English field site with those on our Trinidadian field site.When we tell people that we have written nine monographs about social media around the world, all using the same chapter headings (apart from Chapter 5), they are concerned about potential repetition.However, if you decide to read several of these books (and we very much hope you do), you will see that this device has been helpful in showing the precise opposite.Each book is as individual and distinct as if it were on an entirely different topic.This is perhaps our single most important finding.Most studies of the internet and social media are based on research methods that assume we can generalise across different groups.We look at tweets in one place and write about 'Twitter'.We conduct tests about social media and friendship in one population, and then write on this topic as if friendship means the same thing for all populations.By presenting nine books with the same chapter headings, you can judge for yourselves what kinds of generalisations are, or are not, possible.Our intention is not to evaluate social media, either positively or negatively.Instead the purpose is educational, providing detailed evidence of what social media has become in each place and the local consequences, including local evaluations.Each book is based on 15 months of research during which time the anthropologists lived, worked and interacted with people in the local language.Yet they differ from the dominant tradition of writing social science books.Firstly they do not engage with the academic literatures on social media.It would be highly repetitive to have the same discussions in all nine books.Instead discussions of these literatures are to be found