The 14th July has been celebrated by the french every year since 1789, the year that citizens of France rebelled against the monarchy and stormed the Bastille prison where dissenters (in fact, anyone who disgreed with the way that France was being governed) were held. The storming of the Bastille marked the start of the French Revolution which allowed the people to govern France. The first celebration, in 1790, was called the Fête de la Fédération and was a massive feast and official event.
Formally called La Fête Nationale, it is now a national (public) holiday and is celebrated all over France (as well as many other countries with a large french population) with both official ceremonies, for example on the Champs-élysées in Paris, as well as parties and firework displays (feu d”artifice) in just about every town. There is a tradition (which is permitted by Article 17 of the French Constitution) of pardoning some petty criminals by the state on this day.
What events are being planned for Brittany and Pays de la Loire? How will you celebrate in 2010? Why not add a comment here to let us know?

From Shaun:
Why not combine your 14th July celebrations in the Loire Atlantique with the Fete da la Moule in Pornic?
From Bastille Day:
Do you really know everything about Bastille Day?
Test your knowledge at http://bastille-day.com
From Beattie:
There is a Medievel Festival and Firework display in the old fortified Brittany town of Josselin on 14th July.