For more than a century, strict gun control was possible because firearms were produced in centralized industrial factories. Today, the Fourth Industrial Revolution, combining old and new technologies, threatens to upend this arrangement. An increasing number of hobbyists, "makers," technology provocateurs, and sophisticated criminals are proving that you don't need a factory to make guns anymore. The security challenges of this transformation are increasingly apparent, but the technologies behind it hold tremendous potential, and while ignoring the security implications would entail risks, the costs of new policies also must be evaluated. "Do-it-yourself," or DIY, weapons will bring significant ramifications for First and Second Amendment law, international and homeland security, crime control, technology, privacy, innovation, and the character of open source culture itself. How can a liberal society adjust to technologies that make it easier to produce weapons and contraband? Informative and thought-provoking, carefully analyzes the technical, legal, social, political, and criminological trends behind this challenging new area of illicit weapons activity.