Francois Hollande has become president of France following a ceremony at the Elysee Palace in central Paris.
Mr Hollande is the first Socialist leader of France since Francois Mitterrand left office in 1995.
The 57-year-old was elected to a five-year term in an election earlier this month after voters rejected incumbent Nicolas Sarkozy after only one term.
Mr Sarkozy greeted Hollande on the steps of the palace, and took him inside to transfer nuclear codes and other secret files ahead of a short swearing-in ceremony.
Hollande is due to fly to Berlin later for his first meeting with German Chancellor Angela Merkel.