Knowledge is power and the information behind it must be liberated. Today, more than ever, data has become an important stake in social struggles and the tightening of control over it has not gone without resistance. Social activists around the world are engaging with data in novel ways, whether through investigating tax havens, tracking police misconduct, confronting employers with evidence of wage theft, mapping evictions across the cityscape, or charting the dispossession of Indigenous Peoples of their lands. Social movement groups, labour unions, and community organizations are developing and applying new kinds of technology and programming skills to collect and analyze data in ways that go beyond traditional information access. Drawing on interviews with more than fifty data activists around the world, Mobilizing Data for Justice provides the inspiration that activists need for social justice struggles today.