Hidden beneath the surface of the internet, a new, stark reality is looming--one that cuts to the very heart of our endless debates about the impact of AI. Anthropologist Mary L. Gray and computer scientist Siddharth Suri team up to unveil how services delivered by companies like Amazon, Google, Microsoft, and Uber can only function smoothly thanks to the judgment and experience of a vast, invisible human labor force. These people doing ghost work make the internet seem smart. They perform high tech, on-demand piecework: flagging X rated content, proofreading, transcribing audio, confirming identities, captioning video, and much more. An estimated 8 percent of Americans have worked at least once in this ghost economy, and that number is growing. There are no labor laws to govern this kind of work, and these latter-day assembly lines draw in--and all too often overwork and underpay--a surprisingly diverse range of workers: harried young mothers, professionals forced into early retirement, recent grads who can't get a toehold on the traditional employment ladder, and minorities shut out of the jobs they want. Gray and Suri also show how workers, employers, and society at large can ensure that this new kind of work creates opportunity--rather than misery--for those who do it.