Terrorism, although perhaps known by other names, is not a new phenomenon. It dates back to Roman times and perhaps even further in world history. Caleb Carr says terrorism "is simply the contemporary name given to, and the modern permutation of, warfare deliberately waged against civilians with the purpose of destroying their will to support either their leaders or policies... " In modern times, in the United States, there have been isolated violent acts of citizens against each other, although these acts often were directed toward symbols of the federal government. In the Middle East and other parts of the world, acts of violence against U.S. citizens and military personnel date back into the early 1960's. Some of these acts seem to be almost random in nature. But these events occurred in distant lands of sometimes uncertain locations to the American public, who soon forgot them and their important message. Even though there had been at least one other attempt on the World Trade Center, it was not until 11 September 2001 that successful, large-scale acts of terrorism came to our shores. In 1998, the National Council on Radiation Protection and Measurements (NCRP) formed a Scientific Committee and charged the committee with the task of providing a report on the state of preparation and the potential use by terrorists of radiation and radioactivity. The draft report of the Committee was produced a year in advance of the events of 11 September 2001 and was published in its final form about a month after these terrible events. The report brought together, in one place, information that existed in a number of areas, not all of which were easily accessible. However, there were a number of gaps in the information and in the planning and preparation for such events. These were reflected in a series of recommendations for organization, planning, and training, as well as for research and development in a number of areas. This brief presentation will address a few selected areas that remain a challenge for those preparing for terrorist events involving radioactive materials. More detailed discussions will be provided by the presentations at this NCRP Annual Meeting.