The history section is based on notes taken from the World Book encyclopedia CD-ROM, the official Marseillaise resource at http://www.premier-ministre.gouv.fr and the French Embassy in Fiji.
Following France's declaration of war on Austria and Prussia, the mayor of Strasbourg, Baron de Dietrich, asked army engineer Claude-Joseph Rouget de Lisle to write a marching song. On the night of April 25th 1792, Rouget de Lisle penned the Chant de guerre pour l'armée du Rhin - war song for the Rhine Army, named in honour of the garrison to which he belonged.
The song was published under the name of Chant de guerre aux armées des frontières - Border armies' war song by one François Mireur, who was in Marseille to organise a march of revolutionary volunteers on King Louis XVI's Tuileries palace. The French Embassy in Fiji site describes Mireur as a student from Montpellier whereas the Prime Minister's site casts him as a general of the Egyptian army recruiting volunteers from Montpellier and Marseille. I suspect this is more likely to be true.
Ironically, since Rouget de Lisle supported the monarchy, the revolutionaries adopted the song and sang it with such fervour as they entered the capital, on July 30th 1792, that the Parisians named it La Marseillaise.
It was declared a national song on July 14th 1795 and subsequently banned under the Empire. The July revolution of 1830 reinstated the song, which was rearranged by Hector Berlioz, and it was adopted as the national anthem under the Third Republic in 1879. In 1887 the Ministry of War, after consultation with a specially-appointed commission, adopted what it was to call an "official version" of the song, which was written into the Constitutions of the Fourth and Fifth Republics (1946 and 1958 respectively). Article 2 of the Constitution of October 4th 1958 designates La Marseillaise national anthem of France.
La Marseillaise is divided up into seven verses and a chorus. However at national events, sporting meetings and other occasions when it is played, only the first verse and the chorus are sung. Indeed most French people only know these sections. Personally I like the fourth and sixth verses although they all have a certain style to them. I almost typed je ne sais quoi there but thought better of it.
Today's version is adapted from the 1887 score but in 1974, during President Giscard d'Estaing's premiership, performances of la Marseillaise were played at a slower tempo so as better to reflect the music's origins.
You can see the French lyrics under paroles françaises and my standard translation under English lyrics.
Hector Berlioz's grandiose arrangement of the song now has its own dedicated section on this site: Berlioz.