David Pierre Ruelle (born 20 August 1935 Ghent, Belgium) is a Belgian - French mathematical physicist. He has worked on statistical physics and dynamical systems. With Floris Takens he coined the term strange attractor, and founded a new theory of turbulence. In 1986, he received the Boltzmann Medal for his outstanding contributions to statistical mechanics, and in 1993 the Holweck Prize. In 2004, he received the Matteucci Medal, and in 2006 the Henri Poincaré Prize.

He studied physics at the Université Libre de Bruxelles, obtaining a Ph.D. degree in 1959 (prepared at ETH Zurich). He spent two years (1960 – 1962) at the ETH Zurich, and another two years (1962 – 1964) at the Institute for Advanced Study in Princeton, New Jersey. In 1964, he became Professor at the Institut des Hautes Études Scientifiques (IHES), in Bures - sur - Yvette, France. Since 2000, he is an Emeritus Professor at IHES and distinguished visiting professor at Rutgers University.

Floris Takens (November 12, 1940 - June 20, 2010) was a Dutch mathematician known for contributions to the theory of chaotic dynamical systems.

Together with David Ruelle he predicted that fluid turbulence could develop through a strange attractor, a term they coined, as opposed to the then prevailing theory of accretion of modes. The prediction was later confirmed by experiment. Takens also established the result now known as the Takens' theorem, which shows how to reconstruct a dynamical system from an observed time - series.

Takens was born in Zaandam in the Netherlands. He attended schools in The Hague and in Zaandam before serving in the Dutch army for one year (1960 – 1961). At the University of Amsterdam he concluded his undergraduate and graduate studies. He was granted a doctorate in mathematics in 1969 under the supervision of Nicolaas Kuiper for a thesis entitled The minimal number of critical points of a function on a compact manifold and the Lyusternik – Schnirelmann category.

After his graduate work, Takens spent a year at the IHES, in Bures - sur - Yvette, near Paris, where he worked with David Ruelle, René Thom, and Jacob Palis. His friendship with Palis has taken him many times to the Instituto de Matemática Pura e Aplicada, IMPA, in Rio de Janeiro, Brazil. Their collaboration produced several joint publications.

Takens was a professor at the University of Groningen, in Groningen, Netherlands, from 1972 until he retired from teaching in 1999.