A.Q. Khan was at the center of a multinational nuclear proliferation program, responsible for two successful nuclear weapons programs (those of Pakistan and North Korea), one nascent program (Iran's) and one dismantled program (Libya's). In contrast to more recent terrorists, he was intelligent and educated in a serious technical subject (metallurgy). Nor was he radicalized by external agents. His motives appear to have been personal and nationalist rather than religious. Measures designed to detect Islamist radicalization are unlikely to be effective against future A.Q. Khans; traditional counter-espionage vigilance is required. Even more important, we must recognize that technical training is a strategic good, and its export must be controlled; without a corpus of technically trained people, even the fruits of successful espionage are of little effect.