With almost one billion web pages on the Internet today, a search engine is a necessity at times. But search engines are also forprofit ventures and the financial success of these sites hinges on advertising revenue. One of the ways in which these sites generate income is by selling "keywords" to advertisers. Although there has been only one judicial decision—Playboy Enterprises, Inc. v. Netscape Communications— involving banner ads keyed to trademarks, it will undoubtedly not be the last. This Article argues that despite the invisible nature of this unauthorized trademark use, the common practice of keying a banner ad to another's trademark is a potential violation of the Lanham Act, giving rise to claims for trademark infringement, false designation of origin and trademark dilution.