Do good things come in threes? Not if you’re Google. Heading into the holidays, the company finds itself facing a trio of antitrust cases brought by an overlapping network of state and federal enforcers. That’s a lot to keep track of. Let’s try to sort through some of the biggest questions.

Why are there all these separate cases against Google, instead of just one?

The simplest answer is that Google has a dominant position in multiple markets. This opens it up to different lines of attack that don’t all fit in the same lawsuit. Two of the cases focus on Google’s monopoly in search and search advertising; the third focuses on its control over what you might call non-search advertising.

OK, so what are the cases?

The US Department of Justice filed the first case in October, joined initially by eleven Republican state attorneys general. This is the narrowest of the three lawsuits. It claims that Google has used anti-competitive tactics to protect its monopoly over general search and prevent rival search engines from getting a foothold. Most notably, the complaint describes the lengths Google has gone to to make sure it’s the default search engine on browsers and smartphones—like paying Apple as much as $12 billion each year to make Google the default on Safari and iPhones. With its control over the search market secure, the suit says, Google can rake in more search advertising revenue, which in turn allows it to keep the payouts flowing. The DOJ argues that this amounts to an illegal scheme to maintain Google’s monopoly over search.

What does Google say about that?

In response to the DOJ’s suit, Google says that there’s nothing wrong with the arrangements it has struck, because it’s easy for users to change the default if they want. As the company’s chief counsel put it in a blog post, “people don’t use Google because they have to, they use it because they choose to.”

But why would Google spend billions of dollars each year to be the default if everyone would freely choose to use it anyway?

Great question!

OK, you said there were two cases about Google search. What’s the other one?

The second case about Google search, and the third to be filed overall, comes from a coalition of more than 30 states, led by the attorneys general of Colorado and Nebraska. It essentially makes the same argument as the DOJ lawsuit, plus a few more accusations. (In fact, the states have requested that their suit be combined with the DOJ’s.) The most important new piece is the allegation that Google has used its monopoly over general search—the activity commonly known as Googling—to discriminate against companies in what’s known as the vertical search business, like Yelp or Kayak. The idea is that Google wants people to begin all their searches on Google, rather than going straight to a vertical search site or app. The states argue that Google has accordingly made changes over the years to how search results appear in order to keep more traffic flowing to Google’s own properties rather than vertical search. That puts those vertical companies in a tight spot, since if users don’t easily find them through Google, they may not find them at all. This is illegal, the states claim, because the goal and effect is to entrench Google’s share of the search market, rather than to steer users to the best results.

What does Google say to that?

Google’s public response so far is simple: The changes it has made are simply about making Google search more useful and relevant to users. If that’s true, there’s nothing problematic about what the company has done. The case may ultimately turn on whether the antitrust enforcers can prove that Google had other goals in mind besides customer satisfaction.