Samsung and Apple participate in one of the biggest-ever technology patent trials on Monday, a case with the potential to change the smartphone market.
The companies will lock horns in a federal courtroom in San Jose, California.
Samsung facing potential U.S. sales bans of its Galaxy smartphones and tablet computers. Both sides are seeking financial damages from the other.
Apple sued Samsung last year in San Jose, claiming its smartphones and tablets slavishly copied the iPhone and iPad. The South Korean company countersued. Since then, the two have expanded their fight to courtrooms in other countries.
At this trial in California, Apple is seeking at least $2.53 billion in damages, though U.S. District Judge Lucy Koh could triple that figure if she finds Samsung willfully infringed Apple's patents.
Samsung has rapidly overtaken Apple and Nokia to become the world's largest smartphone maker.
A loss for Samsung could lead to permanent sales bans against products including the flagship Galaxy S III phone.
A loss for Apple could be significant, not only if it were ordered to pay financial damages but also because of the competitive threats.
The companies had initially sought to keep many documents from public view, but Judge Koh rejected the bulk of the requests on July 17.
The case in U.S. District Court, Northern District of California, is Apple Inc v. Samsung Electronics Co Ltd et al, 11-1846.