How is the world being changed by an explosion of big data collected and published about human lives, coupled with increasingly powerful tools that anyone with an internet connection can use to draw conclusions from this data? Online communities of sleuths have made dramatic impacts on society, both positive and negative, from catching criminals and finding missing persons, to digital vigilantism and doxxing. This interdisciplinary course, open to graduate students in any field, will examine the design and use of new technologies for investigation and their impacts on society. Examples will be drawn from diverse domains including history, journalism, human rights, and national security. Potential topics include: crowdsourced investigations, open source intelligence, citizen journalism, social media verification, digital forensics, and legal and ethical perspectives. The course will take a seminar format with extensive reading and student-led discussions and tech demos. The primary grades are participation and a semester-long project to create or study the use of an investigative technology.