Millions of Internet users have fallen in love with the Twitter "microblogging" service, which lets them swap brief text "tweets." Now companies are embracing the service to engage customers, promote products and monitor what is being said about their brands.

Given the passion and high profiles of "Twitterverse" denizens, the service has evolved into a vital early-warning system for businesses seeking to stave off criticism, and as a way to build better relationships with customers. That is why companies need to know Twitter. Embracing it can help a business thrive; ignoring the service could well hurt it.

For companies unfamiliar with Twitter, this book serves as a field guide. They will get a Twitterverse tour, and learn about the dozens of firms big and small that have harnessed Twitter as a powerful, flexible business tool. The bottom line: Twitter means business.