- Italian law cannot compel Amanda Knox to return from the US for the new trial
- The court could declare her in contempt, but that carries no additional penalties
- It is unclear what will happen if she is convicted in a new appeals trial, but Italy can seek her extradition
- It would then be up to the United States to decide if it honors the request
- US and Italian authorities could also come to a deal that would keep Knox in the United States
Reacting to the retrial, Amanda Knox says it is "painful" to have acquittal overturned, but "confident" in the truth.
- Last year, prosecutors filed a motion to appeal against the acquittals, calling the verdicts "contradictory and illogical"
- Italy's top appeal court examined whether there were irregularities which gave grounds for a retrial, rather than assessing the details of the case
- Knox returned to her Seattle-area home after she was released from prison in Italy and had been scheduled to speak publicly about the trial for the first time on American television in April
- The new trial will be held before a court in Florence
Speaking to Sky News, the sister of Meredith Kercher, Stephanie, welcomed today's decision. She said there were "questions still unanswered", and it was "a step towards finding out the truth".
The decision by the Court of Cassation adds a further twist to a long-running case whose initial handling was sharply criticised by independent forensic experts.
Prosecutors accused Amanda Knox and her ex-boyfriend Raffaele Sollecito of assaulting and killing Kercher in 2007.
They were initially found guilty and sentenced to 26 and 25 years in prison respectively.
In 2011, their convictions were overturned and they were released after serving four years.
Today's decision means the Italian ex-boyfriend of Amanda Knox, Raffaele Sollecito, will also face a retrial.
The court heard six hours of arguments yesterday and spent several hours deliberating that - and a handful of other cases - before announcing it would issue a decision this morning.
Italian prosecutors asked the high court to throw out the acquittal in the murder of 21-year-old British student Meredith Kercher.
Italy's top appeals court has overturned the acquittal of Amanda Knox, meaning she will face a retrial for the murder of Meredith Kercher.