A jury has ruled that Samsung should pay Apple $1.05bn (£665m) in damages in an intellectual property lawsuit in the US.
It said that several of Samsung's devices had infringed Apple's software and design patents.
The jury rejected Samsung's claims that several of its patents had been breached and awarded it no damages.
Apple may now seek an import ban of some of its rival's products, blocking them from the US market.
The two firms account for more than half of global smartphone and tablet computer sales.
The nine-person jury at the federal court in San Jose, California had to consider 700 questions about each sides' claim that its rival had infringed its intellectual property.
It rejected the South Korean firm's claim that Apple's intellectual properties were invalid.
It said that Samsung was "wilful in its infringement" in many of the cases.
Not all of Apple's claims were upheld. Based on previous cases, Samsung is likely to appeal.
The iPhone maker had claimed a total of $2.5bn (£1.6bn) in damages. Samsung had sought $519m.
Michael Gartenburg, research director at Gartner, said the verdict could have major ramifications for the wider smart device sector.
"Apple patents being upheld will force the rest of the industry to both innovation and differentiation," he told the BBC.
"That will be a good thing for consumers in the long run. Anyone who was even thinking about borrowing a technology or design from Apple will think twice about it now.
"Apple's point was that it was possible to create an experience that doesn't look like its designs and only Nokia and RIM Blackberry are really doing that right now."
There has been a spate of lawsuits involving mobile-device makers, but this case had been viewed as one of the most significant to date.
This is because of the size of the damages involved, the likelihood it will influence the way future patent licenses are handled, and the insights it has given into both Apple and Samsung's working practices.
Could this be the end of Samsung as a phone manufacturer?
Edited by PsYcHoKiLLa, 24 August 2012 - 11:44 PM.