This introductory chapter presents reindeer pastoralism as a social-ecological system and outlines its essential components. Reindeer herders – the pastoralists of the north, the reindeer and the natural environment of Fennoscandia – are briefly introduced. The chapter describes how different historical, natural and social environments lead to different management forms in Finland, Norway and Sweden. Further, it provides a historical overview of reindeer pastoralism deeply embedded in Sámi and local culture and gives some key statistics of the situation today. Finally, it outlines the major challenges that reindeer pastoralism is facing today within the three Fennoscandian countries. This chapter therefore provides the background for the detailed analyses in the main part of this book.