Today on Decoder, we’re talking about the big Google antitrust trial that’s currently taking place in a federal courthouse. No, not the one you’re thinking of — it’s the second Google antitrust case in just as many months. The company lost a landmark case in August in which a court ruled that it had an illegal monopoly in search.

This time around, the Department of Justice is claiming Google has another illegal monopoly in the online advertising market. 

Unlike the search case, the ads case is both extremely complicated and somewhat harder to see. We all use search all day, and we’re surrounded by online ads all day, but while it’s easy to talk about search, no one really wants to think about how the ads get there or how much they really cost. And there’s added complexity here because of the intricate relationship between Google’s ad products and its search engine, which afforded Google the scale and resources to grow far faster than the competition — especially through aggressive acquisitions.

See, while Google figured out search advertising all by itself, it had to acquire its expertise in many of the other forms of online advertising, like display and video ads, by buying competitors. It then spent many years integrating and combining those companies and their products into a wildly complicated system known as an ad tech stack, basically an all-in-one shop for businesses and websites of all sizes to buy and sell ads, and creating, arguably, the world’s most sophisticated digital ad network.

To hear the rest of the industry tell it, Google maintained the dominance of that network pretty ruthlessly — most people don’t see the side of Google that makes the money, and that side is just as cutthroat and competitive as any big business.

Verge senior policy reporter Lauren Feiner has been at the courthouse in Alexandria, Virginia, basically every day this month to hear testimony from news publishers, advertising experts, and Google executives — and, ultimately, to see whether a federal judge hands the company another antitrust defeat. I brought Lauren on the show this week to help me break it all down and to get her take on which direction she thinks this case is headed next. 

If you want to know more about everything Lauren and I discuss in this episode, check out these stories for deeper context and analysis on the trial and the history of Google’s ad business: