Terrorism and crime threaten the international community and our society more than ever before. Criminal networks and terrorist groups that often operate globally try to hide their illegal activities by using advanced information and communications technology. They communicate easier and form global communities that are hard to track. Fortunately, resources like social media, event logs, phone call logs, web logs, and other time series data, constitute a rich source for knowledge discovery. There is a serious need for innovative techniques and tools capable of achieving the ultimate goal of early warning to help detecting, identifying and neutralizing the source of a threat. Motivated by this need with high social impact, research related to open source intelligence and security informatics is gaining momentum in academia, industry, law enforcement and intelligence agencies. Developing effective knowledge discovery methods, techniques and tools to combat crime and terrorism requires coordinated and intensified collaborations across these communities. The aim of this symposium is to provide a unique international forum for academic researchers, government professionals and industrial practitioners to socialize, share their ideas, and exchange their data, knowledge, and expertise. Conference Topics: The International Symposium on Foundations of Open Source Intelligence and Security Informatics (FOSINT-SI 2015) invites original research submissions on all topics related to the foundations of open source intelligence and security informatics, specifically ,but not exclusively , those listed below: