AdSense is a great program, though Google has given it a confusing name. If they'd called it AdSpace, you'd know right away what it's about: selling advertising space on your website. Despite the nomenclature issue, AdSense (www.google.com/adsense) has become popular with bloggers and other people who run noncommercial sites. You sign up, carve out some space on your pages for the ads (Figure 1), paste a few lines of code from Google into the HTML for your site, and let Google fill in your pages with color-coordinated ads. When somebody clicks one of the ads, Google pays you a fee (the amount varies, and the company doesn't disclose its payments).

Note: AdSense can be tricky for e-commerce sites because you can't fully control which ads appear on your site, and you wouldn't want to run ads for your competitors' merchandise right next to your own displays. You can, however, filter out some ads.

Though you can't decide which ads appear on your site, Google does a very nice job of assessing your pages and supplying ads that might interest your visitors. For example, if you run a site about the history of window treatments, Google is likely to dish up ads for vintage blinds and specialty curtain rods. That kind of relevance is important, because Google doesn't pay you when somebody sees an ad on your site; it pays you when somebody clicks an ad. So you want Google to fill your space with blurbs likely to interest your readers.

The $64,000 question is, of course, how much can you make? The exact answer is: it depends. If your site gets tons of visitors, and you focus on a narrow topic, there's a good chance Google will serve up ads that appeal to a lot of people hitting your site. For example, if you run a popular site devoted to mobile gadgetry, you might make enough to buy a new device every few months. If your site gets sporadic traffic, or more important, if it's not clearly about something, it may be hard for Google to supply highly relevant ads, and you might make enough to cover a box of paper clips every so often.

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Figure 1. Top: On a Google results page, ads from the AdWords program are called sponsored links. They appear above and to the right of the regular results.

Bottom: On other web pages, ads come from the AdSense program and get the label, "Ads by Google."