While we often think of spies and spy networks as a 20th century innovation, the Civil War was filled with both. Men and women on both sides rallied to their respective cause, and volunteered to pass information to either the North or South. The Civil War also saw many innovations in spying, including the use of invisible ink, the use of advanced cryptography, and numerous women risking their lives to act as spies.Also included in this book are prominent "irregulars", by which I'm including people who fought for one side or other with little or no interaction with the official military or political apparatus of their cause. The terms "guerrilla" and "marauder" are also sometimes used, although I've noticed that who one considers a guerrilla or marauder and who one considers a glorious freedom fighter tends to be determined by what side you are on. Irregular seemed like a neutral term to use.This book contains 25 men and women who served their cause as either spies or irregulars, and includes names such as William Quantrill, John Mosby, Rose Greenhow, "Bloody Bill" Anderson, Allan Pinkerton, Lafayette Baker, James Lane and Elizabeth Lew. It also contains 30 black and white photos and drawings.