This introduction examines the relationship between new patterns of migration, inequalities, and border controls in present-day South America. It starts with a historical overview of migration patterns in the twentieth century, and then focuses on the multiplication of flows in the past twenty years. A second part discusses the character of new mobility patterns, such as forced, transit, and circular migrations, and their connections with extractive industries, informality, and labor exploitation. Next, it discusses the link between these migration patterns and changes in state migration policies towards border control. The introduction ends with a description of the book chapters.