How did a journalist find out who was responsible for bombing hospitals in Syria without leaving his desk in New York? How can South Sudanese activists 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 of every kind are being tracked in completely new ways. Human rights abuses, political violence, nuclear weapons deployments, corruption, radicalisation, and conflict, are all being monitored, analysed, and documented. Though 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 human security.This interdisciplinary book presents 18 contributions by prize-winning practitioners, experts and rising stars, detailing what open source investigations are and how they are carried out, alongside 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, humanitarian law, or anyone with an interest in the possibilities and dangers of this new field.