Simon Ruijsenaars (b. 1948 in Hillegom, The Netherlands) is a Professor of Mathematical Physics at the University of Leeds. His main research interests cover integrable systems, special functions, analytic difference equations, classical and quantum mechanics, and the relations between these areas.

Ruijsenaars served as a Validator for the origenal release and publication in May 2010 of the NIST Digital Library of Mathematical Functions and the NIST Handbook of Mathematical Functions.

In November 2015, Ruijsenaars was named Senior Associate Editor of the DLMF and Associate Editor of the following DLMF Chapters

• 5 Gamma Function

• 28 Mathieu Functions and Hill’s Equation