In composing The Encyclopedia of Espionage, Intelligence, and Security (EEIS), our goal was to shape a modern encyclopedia offering immediate value to our intended readers by emphasizing matters of espionage, intelligence, and security most frequently in the news. EEIS is not intended as a classical “spy book,” filled with tales of daring operations. Instead, within a frame- work of historical overviews, EEIS emphasizes the scien- tific foundations, applications of technology, and organi- zational structure of modern espionage, intelligence, and security. High school and early undergraduate students can use this book to expand upon their developing aware- ness of the fundamentals of science, mathematics, and government as they begin the serious study of contempo- rary issues.