Google AdWords remarketing, conducted through the Google Display Network, is a form of online advertising  that enables advertisers to show ads to users who have already visited their site while browsing the web. Remarketing, also known as ad retargeting can be incredibly successful and can dramatically increase your ROI.
How Does Google Remarketing Work?
If you already advertise on Google , all you need to do is add a piece of Google remarketing code, also known as a tag, to pages of their website that they want to have correspond to certain categories; for example, you might create a “toaster” tag on the pages of your site where you sell toasters.
Advertisers can then enter their AdWords accounts and create a campaign and Google ads  tailored for the keyword “toaster.” Visitors who spend time on your page that is “toaster” tagged will have a cookie placed in their browser so that they then see your toaster-targeted ads across the vast number of Google partner sites in the Google Display Network.
Google recommends that when you are starting your first remarketing campaign, you begin by targeting everyone who viewed your homepage. Just remember, that will increase your Google remarketing costs since your ads are being retargeted to more individuals, and you won’t be able to create ads that are quite as targeted. Incorporating the Google remarketing script tags allows you to target more narrowly, and therefore increase relevancy.
Eventually, you can create some useful Google remarketing lists for super-targeted remarketing campaigns; you can choose to show users who have already purchased from your site different ads (30% off your second purchase).
Advantages of Google Ad Retargeting
Google ad retargeting is powerful internet marketing technique because it allows you to stay connected with your target audience, even after they leave your site. In the example above, WordStream uses Google Remarketing on YouTube to reengage a prospect that has visited the WordStream website with a display banner ad. By presenting your ads to visitors even as they browse other parts of the web, you are gaining brand exposure and becoming more recognizable to your target audience, raising trust and making them more likely to purchase from you.
However, keep in mind that users have the option of opting out of seeing your remarketing ads by adjusting their settings in accordance with the AdChoices  program.
Google Remarketing Cost
Your Google remarketing costs will largely depend on your decisions as an online marketing  advertiser—the broader your remarketing campaigns, the higher your costs will be. To keep costs low, use Google remarketing tags in combination with contextual targeting, conversion filtering, frequency capping, etc. This will enable you to create highly targeted remarketing campaigns and increase your ad relevancy. You can also choose between CPC or CPM pricing.
Google AdWords Remarketing: Banner Ads
When you remarket on the Google Display Network, you have the option of creating ads that incorporate text, images, videos, or rich media. For help making customized Google remarketing banner ads, try using the free Google Display Ad Builder . You can choose from a number of pre-existing templates and then customize them for your business, selecting from a variety of Google remarketing banner sizes and formats.
Ad retargeting is a powerful form of Google advertising, allowing advertisers to target and remarket to specific audiences who have visited their site.
Looking to learn more about advertising on Google? Browse WordStream's Google Advertising Resources:
Read and download informative EBooks from the Google AdWords EBook Collection 
Get your existing AdWords account evaluated with the AdWords Performance Grader. 
Create high-performing PPC campaigns with the WordStream Advisor Software .