Contextual advertising, is a type of targeted advertising, for advertisements appearing on websites, and other platforms such as mobile apps, syndication feeds etc. The advertisements are displayed by the ad provider, by means of scanning the host website's content, and selecting ads which match keywords found in the content of the website.

For example if the visitor is viewing website about automobiles, then ads related to automobiles will be displayed on the site. This is done by scanning the website's content, and reading keywords (which will be related to automobiles), and displaying ads like automobile insurance, or cars. If the site is related to holidays or travel, the visitor is likely to see ads related to flight deals.

This is also called in-text, or in-context advertising. The ad network, gives the host, or the publisher, a code, which renders the ad units on the website. The network's crawlers, or bots, then identifies this placement, and scans the website to "read" the content. The content is matched with a keyword based ad database, and matched ads, are then displayed on the placed units.

Google Adsense was the first major contextual advertising network. Since the success of adsense, many players like Chitika, Yahoo! publisher network, Ad Brite, Microsoft ad center have also entered the arena with their own contextual advertising products.

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