How did a journalist find out who was responsible for bombing hospitals in Syria from his desk in New York? How can South Sudanese monitors safely track and detail the weapons in their communities and make sure that global audiences take notice? How do researchers in London coordinate worldwide work uncovering global corruption? What are policy-makers, lawyers, and intelligence agencies doing to keep up with and make use of these activities? In the age of Google, threats to human security are being tracked in completely new ways. Human rights abuses, political violence, nuclear weapons, corruption, radicalization, and conflict are all being monitored, analyzed, and documented. Although open source investigations are neither easy to conduct nor straightforward to apply, with diligence and effort, societies, agencies, and individuals have the potential to use them to strengthen security. This interdisciplinary book presents 18 original chapters by prize-winning practitioners, experts, and rising stars, detailing what open source investigations are and how they are carried out, and examining the opportunities and challenges they present to global transparency, accountability and justice. It is essential reading for current and future digital investigators, journalists, and scholars of global governance, international relations and humanitarian law, as well as anyone interested in the possibilities and dangers of this new field.