A groundbreaking mathematician presents a new model for understanding financial markets Benoit B. Mandelbrot is world-famous for inventing fractal geometry, making mathematical sense of a fact everybody knows but that geometers from Euclid on down had never assimilated: Clouds are not round, mountains are not cones, coastlines are not smooth. To these insights we can now add another example: Markets are not the safe bet your broker may claim. Mandelbrot, with co-author Richard L. Hudson, shows how the dominant way of thinking about the behavior of markets--a set of mathematical assumptions a century old and still learned by every MBA and financier in the world--simply does not work. He uses fractal geometry to propose a new, more accurate way of describing market behavior. From the gyrations of the Dow to the dollar-euro exchange rate, Mandlebrot shows how to understand the volatility of markets in far more accurate terms than the failed theories that have repeatedly brought the financial system to the brink of disaster. The result is no less than the foundation for a new science of finance.