This backgrounder is intended to provide answers to the most frequently asked questions about nuclear terrorism, beginning with a summary of the main nuclear threats facing us today. As an understanding of radiation is essential to this discussion, a section on the subject follows, and includes the main types of radiation and their more common sources. This is followed by a section on the damage that could be expected from the different scenarios, ending with a discussion on what is generally known about how to respond to and prevent these threats. The appendix lists organizations that can be contacted for additional information on the topics discussed and includes specific contacts for both the general public and members of the media.