Fatou Bensouda, a former Gambian justice minister, has been sworn in as the International Criminal Court's new chief prosecutor in The Hague.
She becomes the first African to hold the post.
She is taking over from Argentinian Luis Moreno Ocampo, who is stepping down after nearly a decade in office.
The BBC's Anna Holligan says one of Ms Bensouda's earliest priorities will be bringing Saif al-Islam Gaddafi, the son of the late Libyan leader, to justice.
Ms Bensouda will also be overseeing the ICC's first trial of a former head of state, when the Ivory Coast's ex-President Laurent Gbagbo appears in court.
Liberia's former leader, Charles Taylor, was tried by a UN-backed court trying those responsible for the atrocities during Sierra Leone's civil war.
'Calm and sensitive'
At the swearing-in ceremony in The Hague, Ms Bensouda praised the work conducted by her predecessor and promised to make the victims of crime her priority.
"As I begin my tenure, moving forward in consolidating current practices, the office will continue to forge ahead with its investigations and
