Over the next 10 weeks from Tuesday, federal lawyers and state attorneys-general will try to prove Google rigged the market in its favour by locking its search engine in as the default choice in a plethora of places and devices.
US District Judge Amit Mehta likely won't issue a ruling until early next year. If he decides Google broke the law, another trial will decide what steps should be taken to rein in the California-based company.
Top executives at Google and its corporate parent Alphabet, as well as those from other powerful technology companies, are expected to testify.
The Justice Department alleges the company has used its internet search dominance to gain an unfair advantage against competitors.
Government lawyers say Google protects its franchise through a form of payola, shelling out billions of dollars annually to be the default search engine on the iPhone and on web browsers such as Apple's Safari and Mozilla's Firefox.
Regulators also charge that Google has illegally rigged the market in its favour by requiring its search engine to be bundled with its Android software for smartphones if the device manufacturers want full access to the Android app store.
Google counters that it faces a wide range of competition despite commanding about 90 per cent of the internet search market.
Its rivals, Google argues, range from search engines such as Microsoft's Bing to websites like Amazon and Yelp, where consumers can post questions about what to buy or where to go.
From Google's perspective, perpetual improvements to its search engine explain why people almost reflexively keep coming back to it, a habit that long ago made "Googling" synonymous with looking things up on the internet.
Today, Google's corporate parent, Alphabet, is worth $US1.7 trillion ($A2.6) trillion and employs 182,000 people, with most of the money coming from $US224 billion ($A349 billion) in annual ad sales flowing through a network of digital services anchored by a search engine that fields billions of queries a day.
