Have you heard? All the world's a-twitter!

Twitter is a tool that you can use to send and receive short, 140-character messages from your friends, from the organizations you care about, from the businesses you frequent, from the publications you read, or from complete strangers who share (or don't share) your interests.

As a user of Twitter, you choose whose updates you want to receive — which people you want to follow. In turn, other users can elect to follow your updates. You can send messages publicly for the entire Twitter community, semi-publicly to users whom you approve to receive your messages, or privately from one user to another. You can view these messages, called updates or tweets, either on the Internet or on your cellphone.

Twitter has changed and enhanced the way that people communicate with each other, with brands and companies, and with social movements and initiatives. Twitter has empowered users to raise money for people in need, coordinate rescue efforts in the wake of a natural disaster, and alert authorities to emergencies and illegal activities both domestic and abroad.

Skeptical of what you can say in 140 characters? The first paragraph of the Introduction weighs in at 41 characters. This paragraph? 137.

You may also find, over time, that you communicate more effectively and that your writing becomes shorter and more to the point. You can say a lot within very little space; and because it takes only a little time to read and update, you may be surprised ...

Get Twitter™ for Dummies® now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.