Some people think that colonialism is long over, while others are sure it has never stopped. This book explores a third possibility: not only is colonialism still continuing, but right now it is morphing into possibly its most powerful version yet. This is data colonialism. In 2020 Tierra Común was formed: a network of activists and scholars, mainly from Latin America, to resist colonialism that operates through data and digital technologies. This book was written collaboratively by members of Tierra Común. It is intended as a toolkit for understanding what data colonialism is, who it harms, and how it can be resisted. The book’s theoretical framework explores the historical roots of today’s data practices in colonialism and racism, and the colonial entanglements that shape data extraction and AI like all forms of modern science. It examines key examples of how data practices today operate in colonial ways, and their implications for identity, life and being at the most fundamental level. Nine case studies written by members of Tierra Común show how data colonialism is being resisted practically in many diverse communities across the Americas. The book ends with some reflections on pathways for resistance, a ten-point resistance toolkit, and a lexicon of key terms.