The first digital electronic computer, the ENIAC, was over 100 feet long, with 18,000 simultaneously functioning vacuum tubes. Now virtually every business and home in America has its own compact PC. In 1903 the Wright brothers' airplane, held together with baling wire and glue, traveled a couple hundred yards. Today fleets of streamlined jets transport millions of people per day to cities worldwide. Between discovery and application, between invention and widespread use, there is a world of innovation, of tinkering and improvements and adaptations. This is the world David Mowery and Nathan Rosenberg map out in Paths of Innovation, a tour of the intersecting routes of the technological.