Dear Colleagues, With great sadness, we inform you of the passing of Andrée Ehresmann (née Bastiani) on Friday, August 21, 2026, at her home in Amiens. Andrée Ehresmann played a major role in the category theory community for over sixty years. Born in Nice in 1935, she went as a young woman to Paris to study mathematics and Latin. She completed her doctoral thesis, and later her thèse d'État, in functional analysis, under the supervision of Gustave Choquet. From 1967, she was maître de conférences, and then professor, at the Université de Picardie in Amiens. It was Choquet who, already during her doctoral studies, encouraged her to take up category theory in the form that Charles Ehresmann was developing at that time. She later met Charles Ehresmann, who became her husband, and with whom she collaborated intensively until his death in 1979. Together they established the French school in category theory in Amiens, which became a vibrant research center, known internationally. From 1970 onwards, she was the driving force behind the Cahiers de Topologie et Géométrie Différentielle Catégoriques, which she directed until her passing. Andrée Ehresmann worked in various areas of category theory and pioneered the applications of categorical methods to the modeling of living and cognitive systems, mainly in collaboration with Jean-Paul Vanbremeersch. Her fundamental scientific contributions have been presented in an invited talk by René Guitart at the Séminaire Itinérant des Catégories held in Louvain-la-Neuve to celebrate her 90th birthday (https://www-lmpa.univ-littoral.fr/~sic/wordpress/?page_id=1609). The slides of René's talk are available here: https://www-lmpa.univ-littoral.fr/~sic/Louvain2025/Guitart.pdf On that occasion, she herself participated remotely and presented a talk, in French, about her scientific career: https://www-lmpa.univ-littoral.fr/~sic/Louvain2025/Ehresmann.pdf In the final months of her life, Andrée Ehresmann's health declined rapidly. Those who knew her personally appreciated her vision, leadership, generosity, and constant support of younger researchers. With her passing, the category theory community loses a prominent mathematician and a uniquely dedicated figure who contributed greatly to a historic era of French mathematics. Best regards, Isar Stubbe, Marino Gran, and René Guitart.