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.
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."
Google's AdSense engine, as with everything Google, is rather sophisticated. Rather than simply serving up random ads from its advertiser base, Google works hard to make sure the ads your visitors see are likely to pique their interest.
From the day you start offering ads, the AdSense robot visits on a regular basis, reading through your pages with ads. The robot takes a look at the words you use, the frequency with which you use them, even some of your page structure and formatting (for example, bigger fonts usually signify something important). Then Google uses all this info to figure out which ads your readers will warm to.
Even better, Google takes the language of your site and the location of your visitors into account, serving up language- specific, location-targeted ads for maximum impact. So a visitor from France (or a person browsing the Internet from a Frenchified computer) may see AdWords in French (shown here) or from French companies, while your U.S. visitors see theirs in English, Germans in German, and so forth. (See What Are Google AdWords for an excellent how-to of that service.)
Bottom line: Google may know more about your audience than you do. Use AdSense to work that knowledge to your advantage.
The beauty of AdSense, however, is that it's free—absolutely gratis—to join and run, so you may as well give it a whirl. And the program automatically tailors itself to your site over time, supplying more relevant ads as it gets to know you better or as you change your content. It can take a few months before Google hits the sweet spot with ads that your readers love, but the only thing you have to do is set it up and watch it go to work. (Bear in mind, however, that participating in AdSense doesn't have any effect on your site's rank in Google search results.)
Warning: Don't try to game AdSense. It probably won't surprise you a whit to learn that people have set up sites primarily to showcase ads and draw lots of clicks (and make buckets of money). When Google finds out about these sites (and it often does) it blocks the ads immediately. But dirty play makes the whole system weaker, and it harms not only Google but the people who pay for clicks, too. Don't be part of that damage.
Editor's note: This article was excerpted from Google: The Missing Manual. For everything you need to know to become a Google guru, be sure to check out the latest edition.
Sarah Milstein writes, speaks, and teaches frequently on Twitter. She is also co-founder of 20slides.com, a site for lively, work-related workshops. Previously, she was on the senior editorial staff at O'Reilly, where she founded the Tools of Change for Publishing conference (TOC) and led the development of the Missing Manuals, a best-selling series of computer books for non-geeks. She's written for the series, too, co-authoring "Google: The Missing Manual." Before joining O'Reilly, Sarah was a freelance writer and editor, and a regular contributor to The New York Times. She was also a program founder for Just Food, a local-food-and-farms non-profit, and co-founder of Two Tomatoes Records, a label that distributes and promotes the work of children's musician Laurie Berkner.
Rael Dornfest is Founder and CEO of Portland, Oregon-based Values of n. Rael leads the Values of n charge with passion, unearthly creativity, and a repertoire of puns and jokes some of which are actually good. Prior to founding Values of n, he was O'Reilly's Chief Technical Officer, program chair for the O'Reilly Emerging Technology Conference (which he continues to chair), series editor of the bestselling Hacks book series, and instigator of O'Reilly's Rough Cuts early access program. He built Meerkat, the first web-based feed aggregator, was champion and co-author of the RSS 1.0 specification, and has written and contributed to six O'Reilly books. Rael's programmatic pride and joy is the nimble, open source blogging application Blosxom, the principles of which you'll find in the Values of n philosophy and embodied in Stikkit: Little yellow notes that think.
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