David Belle didn't practice all his parkour stunts. Most of the ones that you see in the film were of him performing the stunt for the first time.
The film was at the subject of a controversy when writer/producer Luc Besson accused cinema chain UGC in the French media of boycotting the film by not showing it in their Parisian suburbs cinemas, and thus trying to stop its intended audience from seeing it. UGC replied that they felt their distribution for the film was up to par and that in any case it wasn't Besson's business to decide which cinemas should or should not carry the film.
Although set in Paris, some of the film was shot in Serbia.