How remarketing works
If you're setting up a remarketing campaign and placing the remarketing tag on your site, you need to follow the Interest-Based Advertising Policy.
In order to participate in remarketing, you'll need to create at least one remarketing list, which is simply a list of web visitors (i.e., anonymized cookie IDs) whom you would like to re-engage with a compelling message.
To do so, add the remarketing tag, a small snippet of code that you get from Ad Exchange, across all your site pages. Many sites have an identical footer for all pages, and this remarketing tag could be placed there.
Once you've added the remarketing tag to your site, you can create remarketing lists for any of your webpages. For example, you could create a remarketing list for visitors to your homepage. The remarketing tag tells Ad Exchange to save visitors to your "Homepage list." When people visit that page, their cookie ID is added to the remarketing list.
An online shopper is looking for new running shoes, so she goes to a FastSneakers.com to browse the different styles. However, she leaves without completing a purchase. Knowing that the shopper is a valuable potential buyer, FastSneakers.com could add the shopper to a "Site Visitor" list. This will enable FastSneakers.com to deliver an ad to this shopper and the other potential buyers on that list with a honed call-to-action that will encourage them to return to the website to complete a purchase.
How does remarketing work?
A pixel is embedded on your homepage (for example) - a pixel is a small, invisible piece of code that tells Ad Exchange to save visitors' cookies to your "Homepage List." As people visit your homepage, their cookie is added to the remarketing list. You can then create a campaign in Ad Exchange that targets messages only to visitors whose cookies are on this list. Your remarketing messages is not shown to people whose cookies aren't on the "Homepage List."
Once you've placed the remarketing tag in the footer of your site (learn how), you can begin to build your lists.
Broad vs. narrow lists
Try to strike a balance between creating very detailed user lists and broader user lists. While detailed user lists let you further target your message, you'll get the most scale and volume with broader lists. Creating relevant and meaningful user lists is the primary key to success for remarketing; if you have questions, please consult with your account manager.
As people browse certain Google services and AdSense/Ad Exchange publisher websites, Google stores a number in their browsers (using a "cookie") to remember their visits. This number uniquely identifies a web browser on a specific computer, not a person. Learn more about cookies.
A remarketing tag is a small snippet of code that you get from Ad Exchange that you can add to your website to start using remarketing.
The remarketing tag will auto detect whether or not the page on your site is secure (whether it starts with http or https), so there's no need to customize the tag based on the type of page you place it on.
Once you've added the remarketing tag to your site, you can define lists for different sections of your site using rules. For example, if you want to define a list for a page of your site where you sell electronics, you can use this rule: "URL contains electronics."
With rules, you can create as many lists as you want without having to add more tags to your sites.