Agios Efstratios or Saint Eustratius (Greek:Άγιος Ευστράτιος), colloquially Ai Stratis (Greek:Άη Στράτης) is a small Greek island in the northern Aegean Sea about 30 kilometres (19 miles) southwest of Lemnos and 80 kilometres (50 miles) northwest of Lesbos. Together with Lemnos and nearby islets it forms the regional unit of Lemnos, part of the Greek archipelagic region of the North Aegean.