France and Germany are marking the 50th anniversary of a treaty that helped to reconcile the two former foes.
The German and French leaders have been holding talks in Berlin and there will also be a joint session of the two countries’ parliaments.
The Elysee Treaty was signed by Charles de Gaulle of France and Germany’s Konrad Adenauer on 22 January 1963.
Despite ups and downs in the relationship, Berlin and Paris have been key shapers of the European Union.
De Gaulle described Europe as “a coach and horses, with Germany the horse and France the coachman”, and the co-operation between the two nations has been the foundation stone of the European project, the BBC’s Europe editor Gavin Hewitt says.
At odds
To celebrate what has been described as a festival of friendship, France and Germany are issuing stamps, coins and other items of memorabilia.
French flags will be flying beside those of Germany in Berlin.
Later on Tuesday, more than 500 French lawmakers will travel to the German capital for the session with the Bundestag.
There will also be a joint cabinet dinner and a concert.
On Monday, German Chancellor Angela Merkel and French President Francois Hollande held talks behind closed doors.
Mrs Merkel said in her weekly podcast on Saturday that she felt “a very great closeness” with Germany’s neighbour.
“When we have come together, then mostly a good new solution has come out of it,” the chancellor said.
However, the two countries remain at odds on several issues, including how to deal with the eurozone crisis.
President Hollande – who is pushing for fresh spending to bolster growth – believes that the Germans are wrong to place such emphasis on austerity and cutting deficits.
On Mr Hollande’s side there is also still bitterness that Chancellor Merkel backed Nicolas Sarkozy so openly during last year’s French presidential elections, our editor says.
The ongoing crisis in Mali is also likely to test the two countries’ relationship.
While Paris has deployed troops in the west African nation to halt the advance of Islamist insurgents, Berlin has been reluctant to be drawn deeply into the conflict.