Zbigniew Ciesielski (Polish pronunciation: [ˈzbiɡɲɛf t͡ɕɛˈɕɛlskʲi]; 1 October 1934 – 5 October 2020[2]) was a Polish mathematician specializing in functional analysis and probability theory.

He served as the President of the Polish Mathematical Society from 1981 to 1983.

He received in 1960 his doctorate from the Adam Mickiewicz University in Poznan with dissertation O rozwinięciach ortogonalnych prawie wszystkich funkcji w przestrzeni Wienera (On orthogonal developments of almost all functions in Wiener space) under the supervision of Władysław Orlicz.

In 1974 he was an Invited Speaker of the International Congress of Mathematicians in Vancouver.

Ciesielski's main areas of research are functional analysis, in particular Schauder bases in Banach spaces, and probability theory, in particular the mathematical theory of Brownian motion.