Open Source Intelligence can be defined as the retrieval, extraction and analysis of information from publicly available sources. Each of these three processes is the subject of ongoing research resulting in specialised techniques. Today the largest source of open source information is the Internet. Most newspapers and news agencies have web sites with live updates on unfolding events, opinions and perspectives on world events. Most governments monitor news reports to feel the pulse of public opinion, and for early warning and current awareness of emerging crises. The phenomenal growth in knowledge, data and opinions published on the Internet requires advanced software tools which allow analysts to cope with the overflow of information. Malicious use of the Internet has also grown rapidly, particularly on-line fraud, illegal content, virtual stalking, and various scams. These are all creating major challenges to security and law enforcement agencies. The alarming increase in the use of the Internet by extremist and terrorist groups has also emerged. The Joint Research Centre has developed significant experience in Internet content monitoring through its work on media monitoring (EMM) for the European Commission. EMM forms the core of the Commission's daily press monitoring service, and has also been adopted by the European Council Situation Centre for their ODIN system. This paper will review this growing area of research using EMM as an example.