One of the key characteristics of the modern world is the ever growing mobility of peoples and freight. Such mobility which is essential for the functioning of modern economies and societies is dependent upon the effective functioning of transportation systems that are threatened by terrorism. Transportation systems present attractive targets but are difficult to defend because of their characteristics and developments such as globalization and intermodalism. This paper discusses the relevance of these issues for the security of both freight and passenger systems and the strengths and weaknesses of the policies that have been implemented to safeguard these systems as well as challenges that still require attention.