This chapter deals with a constitutive part of current developments within AI, namely digital tracking that allows data to be collected and modelled at scale in digital systems in the first place. It defines digital tracking and offers examples of digital tracking across web and mobile platforms. It relates digital tracking to the backend material infrastructure of digital communication systems and discusses how the power of big tech has developed with enhanced capacities for digital tracking and datafication. In doing so, it offers the critical notion of infrastructural power as revealed in the study of digital tracking. Infrastructural power is the ability to exert control over the material underpinnings of an ecosystem. We suggest that infrastructural power is a foundational and increasingly important companion to other forms of power exercised in digital communication systems, and sketch ways forward in unpacking the operational logics and political economy of digital tracking and infrastructural power that are crucial for the critical study of AI.