Alexis Tsipras is sworn in as Greek Prime Minister
26 January 2015 Last updated at 23:55 GMT
The far-left Syriza party, which won Greece's general election on Sunday, has formed an anti-austerity governing coalition with the right-wing party Greek Independents.
The coalition will have a comfortable majority in Greece's new parliament.
Syriza's leader Alexis Tsipras has promised to stand up to Brussels and renegotiate the terms of Greece's massive international bailout.
Gavin Hewitt reports.