French mathematician who received his Ph.D. in 1977 from Ecole Polytechnique. In 1994 he was awarded the Fields Medal for his work on dynamical systems, an area developed by Henri Poincaré to study the stability of the solar system. These techniques are applicable to problems in biology, chemistry, mechanics, and ecology—areas where stability is needed. "Yoccoz puzzles" also produce aesthetically pleasing objects, such as the Julia and Mandelbrot fractal sets. He later taught at the University of Paris.