Ad inventory is the total number of advertising spaces that a publisher or advertising network can make available. In the digital advertising world, ad inventory refers to all available website areas on which adverts can be placed. This includes display adverts on websites, in-app advertising, video adverts or even native adverts that fit seamlessly into the content of the page.

Ad inventory is often managed and sold via ad servers, specialised platforms such as Google Ad Manager or programmatic advertising. Automated auction systems such as Real-Time Bidding (RTB) are used to decide in real time which ad will be delivered in a particular advertising space.

The value of the ad inventory depends on various factors. On the one hand, the reach and the quality of the traffic play a role. A high volume of qualified visitors makes the ad inventory more attractive for advertisers. On the other hand, thematic relevance and the placement of the advertising space can also increase the value. Premium spaces such as the homepage or the first screen page ("above the fold") are generally more expensive.

It is crucial for publishers to optimally monetise their ad inventory without compromising the user experience. For advertisers, it is important to choose the right ad inventory to reach their target groups effectively and efficiently.