Trends & Controversies this issue grows out of a panel discussion at the 2005 AAAI Spring Symposium on Al Technologies and Homeland Security, held at Stanford University in March 2005. Robert Popp, who gave the keynote speech at the symposium, describes a DARPA initiative for dealing with the 21st-century strategic threat triad: failed states, global terrorism, and weapons of mass destruction proliferation. George Cybenko presents a philosophical/strategic viewpoint on national security. K.A. Taipale discusses policy implications of using trusted systems for counterterrorism security and how risk management, decision heuristics, and the presumption of innocence relate to such systems. Latanya Sweeney proposes privacy-aware technology (selective revelation) that allows data about people to be shared for surveillance purposes while protecting their privacy. Paul Rosenzweig points out two major changes in privacy protection in the post-9/11 era: the broadening of the approach to generating privacy policy/rules from a purely top-down process to one that includes a bottom-up component in which privacy is protected through institutional oversight, and a change from a focus on rules to a focus on results. These five articles present a snapshot of the complex interactions between information security and privacy. A comprehensive understanding of such interactions is critical for developing solutions, whether they are technological solutions, political solutions, or both.