On December 11, 2014, Interpol reported on the arrest of seven suspected uranium smugglers by the Moldova police. Carrying out searches in the capital Chisinau and two other towns, the police and the General Prosecutor's office seized 200 grams of uranium-238, 1 kg of mercury, and 1 kg of unidentified radioactive material. The estimated value of the matter is 1.6 million. The suspects are members of an organized criminal network with specialized knowledge of radioactive substances believed to be pursuing to sell this material in Europe. It may potentially be used in the production of a Radiological Dispersion Device (RDD) "a conventional explosive with radioactive material" and could cause massive disruption when obtained by terrorist organizations. Considering the complexity of nuclear terrorism, we fundamentally have to deal with what Bernard Brodie would call "conflicting intuitions". This introduction also presents an overveiw of key concepts discussed in the subsequent chapters of this book.