GoTo.com (renamed Overture in 2001, and acquired by Yahoo! in 2003) created the first search advertising keyword auction in 1998.:119 Google launched its "AdWords" search advertising program in 2000 and introduced quality-based ranking allocation in 2002, which sorts search advertisements by a combination of bid price and searchers' likeliness to click on the ads.:123
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Sponsored search (also called sponsored links, search ads, or paid search) allows advertisers to be included in the sponsored results of a search for selected keywords. Search ads are often sold via real-time auctions, where advertisers bid on keywords.:118 In addition to setting a maximum price per keyword, bids may include time, language, geographical, and other constraints.:118 Search engines originally sold listings in order of highest bids.:119 Modern search engines rank sponsored listings based on a combination of bid price, expected click-through rate, keyword relevancy and site quality.