The official launch of the celebrations of the IHÉS 50th anniversary took place on 27 March in the afternoon in the Marilyn & James Simons Conference Centre, in the presence of Valérie PÉCRESSE, French Minister for Higher Education and Research, many elected representatives and heads of neighbouring scientific institutions, together with Didier and Jean-Loup MOTCHANE, the two sons of the Institute’s founder. Cécile DEWITT-MORETTE (Emerita Professor at the University of Texas) opened the ceremony by recalling historic moments in the Institute’s creation and in particular the famous episode of the meeting between Léon MOTCHANE and Robert OPPENHEIMER. Presentations followed by David RUELLE (honorary professor at IHÉS), Yuri MANIN (Max-Planck Institut für Mathematik and Northwestern University), David MUMFORD (Brown University) Joseph TAYLOR (Princeton University) and Philippe LAGAYETTE (Chairman of the Board of Directors of IHÉS). Valérie PÉCRESSE, who honoured the Institute with her presence, made the closing speech. She then inaugurated the travelling exhibition The Unravelers, based on the book by Jean-François DARS, Annick LESNE and Anne PAPILLAULT, published by Éditions Belin and which had just become available in bookshops. She was also able to congratulate Jacques TITS, who was keen to share this event with IHÉS. The official announcement of the 2008 Abel Prize jointly to John GRIGGS-THOMPSON and himself, had been announced that very morning.