Robert Clark Penner is an American mathematician whose work in geometry and combinatorics has found applications in high-energy physics and more recently in theoretical biology.

[2] Since 2013 Penner has held the position of the René Thom Chair in Mathematical Biology at the Institut des Hautes Etudes Scientifiques.

He then co-discovered the so-called Epstein-Penner decomposition of non-compact complete hyperbolic manifolds with David Epstein, in dimension 3 a central tool in knot theory.

Over several years he developed the decorated Teichmüller theory of punctured surfaces including the so-called Penner matrix model, the basic partition function for Riemann's moduli space.

Extending the foregoing to orientation-preserving homeomorphisms of the circle, Penner developed his model of universal Teichmüller theory together with its Lie algebra.