The web does not live by content alone. There's a reason why you don't need to buy a ticket to surf the internet. There's a reason why the web's resources, diversions, quirks and foibles are free of charge to anyone with a computer and modem. And that reason is advertising.

Advertising has become a ubiquitous force in the virtual world. Most web pages devote the top and/or bottom and/or side panels of their sites to adverts. In fact, the convention has become so predominant that it's a wonder web-surfers continue to respond to the ads. For most people, advertising on the web is like wallpaper in a room: you know it's there, but you don't pay much attention to it. There are other things you came to see.

For advertisers, however, even wallpaper would provide a viable means of spreading the message. As to the internet -- with its presence in the home and the office and the school, with its potential to transmit sounds and moving pictures, with its "new media" appeal -- it's among the juiciest advertising vehicles going.

While most people are aware of the presence of advertising on their PC monitors, they aren't familiar with the many continually-evolving types of internet ads that are available. The most common variety is the banner ad, with its 480x60 pixel size (about 3.7% of the size of an average screen), its catchy logo (remember "Punch the Monkey"?), and its potential to get the innocent surfer to click and catch a direct wave to the advertiser's website. Banner ads have been around since 1994, when they first appeared on HotWired. A younger, smaller cousin to the banner is the button, a form of advertising that appears as a smallish box on the side of the screen. The button performs just like the banner would, but is cheaper because it is not as likely to be seen by the potential customer.

The second-strongest form of web advertising is sponsorship. Usually taking the form of banners or buttons, sponsorships entail a longer-term commitment on the part of the advertiser. Because they are presented as "sponsors" of particular parts of web pages (such as featured articles, chunks of content, or even e-newsletters), sponsorships generally rely on compatibility between the website's content and the advertiser's product.