In-app advertising is advertising that is delivered within mobile applications rather than on mobile websites or desktop. As people spend the overwhelming majority of their mobile time inside apps — games, social platforms, news, utilities, streaming — in-app advertising has become one of the largest and fastest-growing channels in digital advertising. It encompasses the ad formats, technology, and monetization models specific to the app environment.

In-app ads come in several formats suited to the mobile context. Banner ads occupy a portion of the screen, typically at the top or bottom. Interstitial ads are full-screen units that appear at natural transition points, like between game levels or screens. Rewarded video ads offer users an in-app benefit — extra lives, currency, content — in exchange for watching, creating a value exchange that users often welcome. Native ads blend into the app's content and feed. Playable ads let users interact with a mini-version of an advertised app before installing. Each format balances monetization against user experience differently.

For app publishers and developers, in-app advertising is a primary revenue model, often alongside or instead of in-app purchases and subscriptions. Monetizing app inventory programmatically lets developers earn from their user base while keeping the app free or freemium. They connect to demand through SSPs, ad networks, and mediation platforms, using in-app header bidding and SDKs to maximize competition and fill rates for their impressions.

For advertisers, in-app inventory offers reach, engagement, and rich targeting. App environments provide signals like device type, OS, app category, and — with consent — location and behavioral data, enabling precise targeting. In-app ads, particularly rewarded and interstitial video, often achieve high engagement and viewability. For app marketers, in-app advertising is also the primary channel for user acquisition, driving installs measured by cost per install (CPI).

In-app advertising differs technically from the mobile web in important ways. There's no browser, so there are no traditional cookies; instead, the ecosystem relies on mobile advertising identifiers (like Apple's IDFA and Google's AAID) and SDK-based integrations. This has significant implications as privacy changes — notably Apple's App Tracking Transparency, which requires user opt-in for the IDFA — reshape how in-app targeting and measurement work, pushing the industry toward contextual signals, SKAdNetwork-style aggregated measurement, and first-party approaches.

Challenges in the channel include fraud (install fraud, SDK spoofing, and invalid traffic are persistent threats requiring mobile measurement partners and anti-fraud tools) and the constant tension between monetization and user experience — too many or too intrusive ads drive uninstalls.

For both advertisers seeking mobile reach and developers seeking revenue, in-app advertising is indispensable. It's where attention lives on mobile, and mastering its formats, identity dynamics, and fraud protections is essential to capturing value in the app economy.