YES was founded as the European Community Organisation of Socialist Youth (ECOSY) in November 1992 in Oegstgeest/The Hague. The preparatory committee consisted of Philip Cordery (MJS, France), Joris Jurriëns (JS-PvdA, Netherlands), Jens Geier (Jusos, Germany), Giustina Magistretti (Italy) and Pascal Smet (Belgium).
Before 1992 the European activities had been coordinated inside Iusy, especially in the European Leaders Meeting. The foundation of ECOSY had been controversial. In particular, the Austrians and the Swedish promoted an all-European organisation, including the non-EU members.
The European Socialist Youth (Esy), founded in parallel, was only a weak organisation, a short time later renamed as European Committee, one of the Iusy continental committees.
The organisation's name was changed to Young European Socialists (YES) at the 11th Congress in Bommersvik in 2013.