Banner ads are image-based rather than text-based and are a popular form of online advertising. The purpose of banner advertising is to promote a brand and/or to get visitors from the host website to go to the advertiser's website.

Banner advertising, also called display advertising, consists of static or animated images or media and are usually placed in high-visibility areas on high-traffic websites. Banner advertising is attractive because it can help create brand awareness, generate leads and re-target an audience (such as giving a visitor a chance to sign up for a newsletter or free trial before they click away).Traditional banner advertising like the example above has expanded to other forms, such as Facebook Ads and Instagram Sponsored Ads. Facebook and Twitter account for roughly one-third of online display advertising spending. The trend in online advertising has seen digital display ad spending surpass that of search-based ads in recent years. As of 2018, roughly one-fifth of all online ad spending goes to digital display ads, such as banner ads and similar advertisements.

Ad networks are in charge of matching advertisers to websites that want to sell advertising. They keep track of what advertising space is available and match it with advertiser demand. The technology that enables ad networks to do this is a central ad server, which selects specific ads that are tailored to the website's visitor based on keywords from the visitor's search and website viewing behavior or based on the overall context of the host website content.