Wikileaks founder Julian Assange is due to begin his court battle against extradition from the UK to Sweden.
He faces allegations of sexual assault against two women, which he denies.
Mr Assange is expected to argue Swedish prosecutors had no right to issue a warrant for his arrest because he has not yet been charged with any offences.
At the extradition hearing, in London’s Belmarsh Magistrates’ Court, his lawyers will also challenge the move on human rights grounds.
Mr Assange’s legal team, led by Geoffery Robertson QC, is expected to argue that if their client is forced to return to Sweden he could be extradited to the US, or even Guantanamo Bay, to face separate charges relating to the publication of secret documents by Wikileaks.
He fears he could face the death penalty as a result, his defence says.
BBC legal affairs correspondent Clive Coleman suggests that Mr Assange’s lawyers will focus their defence on technical arguments, such as that the Swedish prosecutor in this case is not a recognised judicial authority.
They will also say that the extradition is being sought for Mr Assange’s questioning, not prosecution, meaning the Swedish authorities could ask for him to questioned by UK police, or via the internet, instead.
The defence team will also put forward human rights issues, by suggesting that three of the offences alleged against Mr Assange are not extradition offences.
And our correspondent also said he understood it would be argued that Mr Assange would not get a fair trial in Sweden, because rape cases in that country are customarily held without a jury and in secret.
The whistle-blowing website has been used to publish leaked US diplomatic cables, as well as other sensitive material from governments and high-profile organisations.
Prosecutors will make the case that Mr Assange – a 39-year-old Australian – must be extradited to face charges of rape and sexual molestation under Swedish law, following accusations by two women.
His lawyers will say that the European Arrest Warrant under which he has been detained is invalid because he is only being asked to provide his account of events, but has not yet been charged.
They say he has already offered himself for questioning and extradition is not necessary.
Mr Assange was released on bail by a High Court judge just before Christmas after spending nine days in Wandsworth prison.
He denies sexually assaulting two female supporters during a visit to Stockholm in August.
Mr Assange and his supporters claim the inquiry is politically motivated.
The extradition hearing is expected to last two days.