It is with great sadness that we learned of the death of Jean‑Claude Le Guillou on 6 January 2026, at the age of 86.
Jean‑Claude Le Guillou worked as a professor and researcher at the Université Pierre et Marie Curie (Paris VI), then at the Université de Savoie and at the LAPP in Annecy.
A theoretical physicist specializing in statistical field theory, phase transitions, and strongly correlated fermions, he regularly visited the Service de physique théorique du CEA Saclay CEA from the early 1970s to the early 1990s, actively collaborating with the SPhT researchers.
In particular we cite his numerous works with E. Brezin and J. Zinn‑Justin on calculating critical exponents using field‑theory methods, as well as his condensed‑matter research together with Th. Jolicoeur.
The Institute of Theoretical Physics as a whole joins in the sorrow of his family and loved ones.