L'Institut du Monde Arabe, Paris by renowned French architect Jean Nouvel.
This is the building that made him famous - well, in the architectural world at least :-)
The fascinating bit for me about this building is the moving brise-soleil facade which, rather like the lens of a camera, controls the amount of light entering the building.
If you look closely you can see that some of the squares are more open than others. The centre of each square is just like the aperture blade system of a camera lens.
Here's Wikipedia's description: "The motifs are actually 240 motor-controlled apertures, which open and close every hour. They act as brise soleil to control the light entering the building. The mechanism creates interior spaces with filtered light — an effect often used in Islamic architecture with its climate-oriented strategies."