The case is about intellectual property, but the key issue at stake on Wednesday is over a so-called “preliminary injunction.” Here’s a plain English guide to how this works, and what will happen at the hearing.

What’s a preliminary injunction, and why is it a big deal?

In its lawsuit against Uber, Google’s Waymo unit is seeking two things: 1) damages (or what we would call money); 2) a temporary order to shut down Uber’s R&D work while the court gets to the bottom of the intellectual property issues.

Today’s hearing is about the second of those things. If the court sides with Google and issues the preliminary injunction, Uber will have to suspend work on its self-driving cars for months or even longer. This would be a devastating delay for Uber because several companies are also racing to be first in the next generation of auto technology.

Where and when does the hearing take place?

Things kick off bright and early. At 7:30 a.m. PT, U.S. District Judge William Alsup will conduct a closed door session in which Google and Uber will ask for certain parts of the hearing to be kept under seal. Then at 9 a.m., the actual hearing will begin before the public. The proceedings take place in federal court at 450 Golden Gate Avenue in downtown San Francisco.

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What must Google do to get a preliminary injunction?

Judges don’t hand out these things willy-nilly, especially because they haven’t heard all the evidence in the case. (Hence the term preliminary.) In deciding whether to grant the preliminary injunction, U.S. District Judge William Alsup will apply a test that balances four factors. Here they are (my highlights):

1) there’s a likelihood of irreparable harm; 2) the balance of harm favors Google; 3) Google has a likelihood of success on the merits of the case; and 4) that the public interest favors the granting of the injunction.

As Inside Counsel notes, the most important of these is the “irreparable harm” factor. In this case, it means Google will have to show that it will suffer a permanent injury if Uber is allowed to keep working on its cars while the rest of the case goes forward. The company will basically say, “Please judge, Uber stole our trade secrets and will get an unfair advantage unless you shut them down right now.”

Uber, meanwhile, will try to counter this by saying there’s no risk of “irreparable harm.” As Recode points out, the company will claim Google knew about the alleged trade secret theft for a while and took its sweet time going to court—suggesting Google didn’t consider this “irreparable” at all.

What will the Judge decide? And when?

Judge Alsup could rule today from the bench, issuing the preliminary injunction and then providing written reasons later on. Or he may take some to think about it, and then issue a written ruling announcing his decision in a few days or weeks.

As for the outcome, it’s too soon to say, though the judge could drop some hints during the course of the hearing. And while the bar to getting a preliminary injunction is pretty high for Google, things don’t look great for Uber based on the alleged facts of the case—including an employee who allegedly made off with 14,000 Waymo files—and Alsup’s earlier comment that the employee’s refusal to testify looks bad for Uber.

Can Uber appeal if it loses?

Yes, even though a preliminary injunction is only a temporary measure, Uber could still appeal. But it would be an uphill battle. As Inside Counsel notes, an appeals court will only step in if a judge really missed the mark:

The standard of review used by most courts, including the federal court system, is an “abuse of discretion” standard. Typically, an injunction will be overturned on appeal only if there has been a misapplication of substantive law or the four-factor preliminary injunction standard, the injunction was based on a clearly erroneous finding of material fact or the four-factor test was applied in such a way that it resulted in an abuse of discretion.

Once again, recall that losing at today’s hearing doesn’t mean Uber has lost the whole case. But a preliminary injunction would have a huge impact, and would likely force Uber into some sort of settlement.