From 1958 to today
The early years: 1958 - 1969
The mathematics group at Orsay was founded by Hubert Delange and Jacques Deny in 1958. At the time, it was under the umbrella of both Paris and Orsay, in a department headed by Henri Cartan until 1964.
Léonce Lesieur and Bernard Malgrange arrived in 1960, followed by Jean-Pierre Kahane in 1961, André Néron, Pierre Samuel, then Jean Cerf in 1964, Georges Poitou, Michel Demazure and also Paul Malliavin. Henri Cartan and Gustave Choquet arrived in 1969. Henri Cartan then arranged to have Valentin Poenaru, Harold Rosenberg, and Laurent Siebenmann come too.
Building a department: the 1960s
More organized mathematical activity at Orsay from 1962 onwards came in the form of an analysis seminar which then became the harmonic analysis seminar, and in parallel Jean-Pierre Kahane initiated the constitution of a mathematics library. In number theory at the time, activity revolved around the Institut Henri Poincaré in Paris, but a strong contribution came from Orsay too (the Delange-Pisot-Poitou seminar). Activity in topology got underway with Jean Cerf, followed by Valentin Poenaru, Harold Rosenberg, and Laurent Siebenmann. Algebraic geometry research began, with Michel Demazure at its heart. Partial differential equations were not an early focus, except when it came to potential theory.
Growing bigger: the 1970s and 1980s
The big expansion of the department came around 1970 when teams were set up (5 CNRS research units), which led to new seminars and activities. This was the period when numerical analysis arrived in Orsay—initially linked to functional analysis (Jacques Deny and Roger Temam), and probability theory (Didier Dacunha-Castelle).
During this period, Orsay expanded at all levels: students, PhDs, post-docs, and professors. Work on dynamic systems did not kick off until the late 1980s.
On the way to today’s department: the 1990s
From 1992 to 1995, the mathematicians of Orsay benefited from another huge expansion plan and the creation of a doctoral school.
In 1998, the five research units merged into a single CNRS mixed research unit, while the library took on the status of a CNRS mixed support unit.