Remarketing is a relatively new concept that allows business owners to better tailor their advertisements through Google AdWords to their customers. When a customer views a site, their previous browsing is taken into account and the original site owner can find their site targeted to the customer more often. These customers will then have a greater awareness of the original site, and are more likely to return. This option is now being offered inside Google Analytics accounts that are attached to Google AdWords accounts. One minor change in the code embedded for Analytics is needed, and this change will allow for information collection from DoubleClick when the cookie is present. This cookie is what allows for remarketing to occur.
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Remarketing Now Available With Google Analytics – Marketing Land