The Gymnasium at Eretria is one of the best examples of a palaestra from the early Hellenistic period. This paper presents results from fieldwork carried out by the Swiss School of Archaeology in Greece in 2015 and 2016 that yielded important new insights for the chronology, plan, and function of this complex. The building was constructed around 330–320 BCE as a palaestra with two differently sized courtyards. The courtyards were probably conceived for use by different age groups. The construction period of the palaestra coincided with the introduction of the ephebeia in Eretria. The palaestra was remodeled several times, with a particular focus on improving its bathing facilities, and was finally abandoned around 100 CE when the ephebeia lost its importance.