A quarter of all U.S. startups, and more than half of those in Silicon Valley, were started by immigrants from 1995 to 2005. However, a shortage of H1-B visas for science, engineering and computer researchers is threatening that trend, says innovation researcher Vivek Wadhwa. "The reality is, if we just fix that one issue about the numbers of visas, the problem would likely fix itself. It's that simple," he says.