As outlined in the official complaint:
"Google is the monopoly gatekeeper to the internet for billions of users and countless advertisers worldwide. For years, Google has accounted for almost 90% of all search queries in the United States and has used anticompetitive tactics to maintain and extend its monopolies in search and search advertising."
The filing alleges that Google maintains its market dominance by entering into exclusivity agreements to be the default search product on various devices and platforms, then uses its profits to "buy preferential treatment for its search engine on devices, web browsers, and other search access points".
That, essentially, keeps other search players out of the market.
Google has issued a response to the legal filing, calling it "deeply flawed" and outlining the various ways in which people can opt out of using Google's products.
As per Google:
"People use Google because they choose to, not because they're forced to, or because they can't find alternatives."
As noted by Columbia University law professor Timothy Wu, the case is similar to the one brought against Microsoft in 90s, which alleged that Microsoft was violating antitrust law by bundling Internet Explorer with Windows, and effectively freezing out other web browsers by default. The parallels here are fairly clear - however that case also shows, in retrospect, that the incumbent technology can be superseded, with Google's Chrome now the dominant search engine, even though Microsoft Edge is the default browser on most PCs.
Microsoft eventually settled its case with the Justice Department in 2001, but the courtroom battle took years to culminate in an agreement.
Google could be in for the same, though it's interesting to also note that this complaint is different to the once raised by the House Judiciary Committee earlier this year, in which Google was accused, among other things, of using its market power to reduce traffic to competitor products.
What will that mean for Google's day-to-day operations? Well, likely nothing, though it may result in a change in the laws around how Google can formulate agreements to become the default browser on devices.
Google has warned that the action could eventually raise the prices of phone and tablets, while "artificially propping up lower quality search services". But from a practical standpoint, the action will likely have little impact on Google's core operations - though opening up the market could lead to more competitors in search.
The case is likely to go on for some time.