Nessim Sibony (20 October 1947[1] – 30 October 2021[2]) was a French mathematician, specializing in the theory of several complex variables and complex dynamics in higher dimension.

Sibony received in 1974 his PhD from the University of Paris-Sud with thesis Problèmes de prolongement analytique et d'approximation polynômiale pondérée.

Independently of Adrien Douady and John H. Hubbard, Sibony proved in the 1980s that the Mandelbrot set is connected.

[4] In 1990 he was an Invited Speaker with talk Some recent results on weakly pseudoconvex domains at the ICM in Kyōto.

[5] He was a senior member of the Institut Universitaire de France from 2009 to 2014.