Humanitarian aid has been present in some form throughout human history, yet the modern concept of humanitarian aid has only truly emerged since the later half of the 20th century. Through a complex progression of world events and largely brought about in response to armed conflict, modern humanitarian aid is provided by a multitude of organizations and actors. The purpose of this chapter is to provide a brief overview of the history of humanitarian action, a review of the principles of humanitarian aid and an overview of the major documents which delineate those principles.