Germany's first mass lawsuit begins when 450,000 owners of diesel Volkswagen cars take on the company.
They claim that they are due to compensation for being sold cars based on misleading emission data.
The scandal has already cost VW 30 billion (26.6 billion pounds).
It has met class action lawsuits in the United States and Australia, but this is the first time Germans could pursue group demands since the law was amended last year.
This trial will determine legal points, and the claimants will later be able to file follow-up claims for damages if they succeed.
The trial at Braunschweig Higher Regional Court, about 20 kilometers from VW's headquarters in Wolfsburg, is likely to last for several years.
Some of VW's settlements to date include a deal to buy back 500,000 cars in the United States, where it has been agreed to pay more than $ 25 billion.
In Australia, the company will pay $ 1[ads1]27 million (£ 70 million) to compensate the owners and pay them $ 1400 apiece.
Last week, it was revealed that three current and former Volkswagen executives were being sued for market manipulation in connection with the diesel emissions scandal.
CEO Herbert Diess, chairman Hans Dieter Pötsch and ex-manager Martin Winterkorn did not inform investors early enough on the economic downturn, German prosecutors say.
In 2015, the company admitted to using illegal software to cheat on emissions tests. VW said it was confident that these claims would prove baseless.
This can be a landmark lawsuit – and when it comes to the large number of claimants, there is certainly attention. But that may not be the biggest concern for Volkswagen right now.
Unless there is a settlement, the legal process is likely to take years – VW expects it to take at least four. Even if they win, car owners will have to go back to court to get compensation.
Meanwhile, VW's chairman and CEO are both fighting criminal charges for alleged market manipulation related to the diesel scandal.
Volkswagen itself faces the possibility of hefty fines from the EU, after being accused of cooperating with other manufacturers to delay the introduction of emission control technology.
It's safe to say that the lawyers are already pretty busy at the moment. And in the meantime, the company is trying to become a leader in the electric car market.
Against this background, the class action lawsuit may seem like an annoyance at the moment.