Cross-device attribution refers to the particular difficulty of tracking user behavior across different devices, such as smartphones, tablets, and computers. One of the main challenges of this method is determining how an initial interaction on a mobile phone can influence a subsequent purchase or conversion made on a computer. This process can involve complex journeys spanning more than two devices. Measuring cross-device attribution is inherently complex due to the difficulty of tracking users from one device to another. This represents a major challenge for both advertisers and advertising platforms seeking to demonstrate their effectiveness.

Companies like Facebook and Google are in a privileged position in the field of cross-device attribution because they can track their users as they move from one device to another using identifiers and authentication data. For sectors like tourism, where offers are often discovered on mobile devices while the purchase is generally made on a computer, the concept of cross-device attribution is particularly important.

The issue of cross-device attribution was extensively discussed at an event on online advertising accounting. The technical aspects of this method and the challenges posed by the elimination of third-party cookies are complex topics that highlight the technological and ethical limitations of cross-device attribution.