former French pharmaceutical company founded in 1999 through the merger of the German firm Hoechst (Hoechst Aktiengesellschaft) and the French company Rhône-Poulenc (Rhône-Poulenc SA). With headquarters in Strasbourg, France, Aventis was the product of the first transnational merger to combine large rival companies from France and Germany. It became part of the French pharmaceutical conglomerate Sanofi-Aventis in 2004.