Though Charles Ehresmann had extensively used the notion of groupoids (taken from Brandt, 1926) from his 1950 paper on connections?? up, the first paper where he explicitly used categories is "Gattungen von lokalen Strukturen (Jahresb. d. Deutschen Math.1957) which is at the basis of many of his and my later works From 1963 on, he published abstracts of his articles on category theory (e.g. on'structured' or 'internal' categories),in a series of "Notes aux Comptes-Rendus de l'Acad??mie des Sciences" and they were classified in the Section "Alg??bre Homologique". At that time, he asked if if was not possible to create a new more adapted Section called "Th??orie des Cat??gories", but it was refused. It is only in 1966 that the Acad??mie created a Section called "Alg??bre des cat??gories" (which contained his last Notes). (For references, cf. his "Oeuvres Compl??tes et Comment??es" freely downloadable on https://ehres.pagesperso-orange.fr/C.E.WORKS_fichiers/C.E_Works.htm .) Kind regards Andree [For admin and other information see: http://www.mta.ca/~cat-dist/ ]