- Eric Rains (Caltech)
- Lie Theory
- 4th Nov 2006 to 13th Nov 2006
- Sarah Rees (Newcastle, UK)
- Geometric Topology
- 14th Dec 1991 to 21st Dec 1991
- Miles Reid (Warwick)
- Algebraic Geometry
- 14th Dec 2000 to 15th Jan 2001
- 16th Jul 2001 to 10th Aug 2001
- 1st Sep 2005 to 14th Sep 2005
- Herman J.J. te Riele (CWI. Amsterdam)
- Comp. Number theory
- 1st Oct 1995 to 23rd Oct 1995
- Carlos Rito (Univ. de Trás-os-Montes e Alto Douro, Portugal)
- Algebraic Geometry
- 10th Jul 2023 to 4th Aug 2023
- 19th Aug 2024 to 14th Sep 2024
- David Roberts (University of Minnesota)
- Number theory
- 10th Jun 2013 to 10th Jul 2013
- Bernardo Rodrigues (KwaZulu-Natal)
- Coding theory
- 4th Dec 2012 to 21st Dec 2012
- Colva Roney-Dougal (St. Andrews)
- Geometric Topology
- 29th Nov 2001 to 28th Nov 2002
- 29th Nov 2002 to 28th Nov 2003
- 21st Jan 2005 to 13th Feb 2005
- 13th Nov 2006 to 1st Dec 2006
- 26th Feb 2018 to 30th Mar 2018
- Dan Roozemond (TU Eindhoven)
- Lie Theory
- 30th Apr 2006 to 31st Dec 2006
- Amnon Rosenmann (Ben-Gurion)
- Group Theory
- 1st Feb 2005 to 28th Feb 2005
