Benoit Mandelbrot, father of fractal geometry, revolutionised our understanding of the models of modern financial theory. This new edition includes material on the current market crisis, calling for an end to the tunnel vision of our bankers whose over-confidence in their understanding of markets ended in catastrophe. Fractal geometry is the mathematics of roughness: how to reduce the outline of a jagged leaf or static in a computer connection to a few simple mathematical properties. With his fractal tools, Mandelbrot has got to the bottom of how financial markets really work. He finds they have a shifting sense of time and wild behaviour that makes them volatile, dangerous, and beautiful. In his models the complex gyrations of the FTSE 100 and exchange rates can be reduced to straightforward formulae that yield a much more accurate description of the risks involved.