- Tanja Lange (Eindhoven)
- Cryptography
- 9th Dec 2019 to 13th Dec 2019
- Alan Lauder (Oxford)
- Arithmetic Geometry
- 11th Feb 2013 to 24th Feb 2013
- Reinhard Laue (Bayreuth)
- Combinatorics
- 13th Jan 2009 to 17th Jan 2009
- Gregoire Lecerf (École Polytechnique, Paris)
- Commutative Algebra
- 17th Aug 2000 to 15th Sep 2000
- Charles Leedham-Greene (QMUL)
- Group Theory
- 1st Sep 1988 to 15th Oct 1988
- 22nd Aug 1994 to 23rd Sep 1994
- 11th Nov 1996 to 29th Nov 1996
- 1st Jan 1999 to 4th Apr 1999
- 4th Sep 1999 to 12th Sep 1999
- 28th Nov 1999 to 4th Dec 1999
- 15th Apr 2007 to 26th May 2007
- Dimitri Leemans (Bruxelles Libre)
- Group Theory, Incidence Geometry
- 26th Mar 1997 to 12th May 1997
- 28th Mar 1999 to 1st Jun 1999
- 1st Apr 2001 to 5th May 2001
- 1st Jan 2002 to 31st Jan 2002
- 15th Sep 2007 to 12th Dec 2007
- Arjen Lenstra (Citibank, NY)
- Comp. number theory
- 1st Jan 1991 to 15th Feb 1991
- 15th Dec 1995 to 31st Jan 1996
- Reynald Lercier (CELAR)
- Comp. number theory, Cryptography
- 1st Dec 1997 to 31st Dec 1997
- Pascal Letard (Bordeaux)
- Comp. number theory
- 4th Apr 1994 to 15th Jul 1994
- Zhibin Liang (Beijing Normal)
- Number Theory
- 2nd Sep 2011 to 8th Nov 2011
- Frank Luebeck (RWTH, Aachen)
- Lie Theory
- 7th Feb 1999 to 10th Apr 1999
- Klaus Lux (Tuscon)
- Representation Theory
- 18th Sep 1992 to 20th Sep 1992
