Julian Assange's lawyers say they will argue in court that the WikiLeaks' founder cannot be sent from Britain to the U.S. to face spying charges.
Because of a treaty between the two countries that bans extradition for political offenses.
The 48-year-old faces 18 counts in the U.S. - including conspiring to hack government computers and violating an espionage law.
If convicted, he could spend decades in prison.
Protesters demanding Assange's release gathered outside London's Westminster Magistrates' Court.
While Assange's lawyer outlined some of the evidence they plan to put forward at the full hearing, set to start on February 24th.
Aside from the treaty, Assange's team could bring up to 21 witnesses to testify.
Other arguments would feature medical evidence and details from the case of Chelsea Manning - the ex-Army intelligence analyst and whistleblower convicted of espionage for her massive document dumps through WikiLeaks.
Assange, who was seen via videolink from prison Thursday (December 19), will be also interviewed by a Spanish judge when he appears in person, over allegations that he was subject to electronic eavesdropping during his asylum in the Ecuador embassy.