Friday's civil wedding will be followed a day later by a religious ceremony at the royal palace on the Mediterranean.
Ms Wittstock, 33, who swam in the 2000 Sydney Olympics, will become Her Serene Highness, Princess Charlene.
The palace has denied reports in the French press that Ms Wittstock was getting cold feet about the wedding.
The guest list includes heads of state and royalty, from French President Nicolas Sarkozy to the heir to the Spanish throne, as well as fashion designer Karl Lagerfeld and supermodel Naomi Campbell.
prince albert
prince albert
prince albert
prince albert
prince albert
