Google ads power the internet ecosystem. Businesses rely on ads to find their customers. Publishers and creators rely on digital advertising as their source of revenue. Finally ads enable end users to reach internet content for free. In this talk, I will provide a high-level overview of the Google ads system. The talk will focus on different machine learning systems that power Google ads: the challenges these models face, the scale at which they operate, how they evolve, and some of the state-of-the-art techniques they leverage. I will highlight how these models classify internet content, how they decide when and what ads to show, how they help advertisers reach the right audience, and how they help us protect users.