Most digital advertising happens in-app. There are application publishing platforms which carry an estimated 6.4 million apps live. Smartphone users spend considerable amount of time everyday with mobile apps. Marketers have made app advertising and integral aspect of their marketing strategy. It is thought that this is the best way to reach the youngsters. However, even the senior citizens and women too have seen using the smartphones. Stay-at home mothers too use gaming apps. There are working professionals who use OTT content and sports apps. To begin with, it was believed that it is difficult to measure the effectiveness of mobile ads. Advanced technologies enable now advertisers to track in-app ads. The ads are measured against norms such as impressions, completed views, CPI, attributions etc. in real-time. It is possible to compare the behaviour before and after an app installation. Digital ads are either in-app ads or web/WAP ads. In-app ads have a higher viewability than the web ads. There are app install campaigns of many advertisers. Such campaigns drive the in-app advertising. Digital video ads are popular in-app ads. This video consumption is driven by in-app vide ads. Though gaming apps were to begin with popular with the youngsters, they have now been adopted by all ages and genders. In-app ads will show expontial growth over the next couple of years. Marketers are now designing ad compaigns based on in-app ads.