Cross-border solidarity has captured the interest and imagination of scholars, activists and a range of political actors in such contested areas as the US-Mexico border and Guantanamo Bay. Chandra Russo examines how justice-seeking solidarity drives activist communities contesting US torture, militarism and immigration policies. Through compelling and fresh ethnographic accounts, Russo follows these activists as they engage in unusual and high risk forms of activism (fasting, pilgrimage, civil disobedience). She explores their ideas of solidarity and witnessing, which are central to how the activists explain their activities. This book adds to our understanding of solidarity activism under new global arrangements, and illuminates the features of movement activity that deepen activists’ commitment by helping their lives feel more humane, just and meaningful. Based on participant observation, interviews, surveys and hundreds of courtroom statements, Russo develops a new theorization of solidarity that will take a central place in social movement studies.