Sulęcin (Polish pronunciation: [suˈlɛɲtɕin]; German: Zielenzig) is a town in western Poland with 10,117 inhabitants (2019), the capital of Sulecin County, since 1999 in Lubusz Voivodeship.

The town was mentioned for the first time in documents in 1241 when bishop Henry granted nobleman Mrotsek the right to build a new settlement for Germans.

[2] Until the 12th century under dominion of the Silesian line of the Piast dynasty, the town with 10 surrounding villages was handed over by Polish Duke Henry I the Bearded to Mroczko from Pogorzela, who in 1244 gave it to the Knights Templar.

It was destroyed by the Polish army of Duke Bolesław the Pious in retaliation for a Brandenburg invasion.

Duke Henry IV the Faithful confirmed the rights of the Knights Hospitaller to the town and the castle, by virtue of a document issued in 1322 in nearby Lubniewice.

In 1419 Sulęcin suffered a severe damage, as the Hussite Wars reached the city.

After World War I a number of companies involved in timber processing set up in the town.

After Nazi Germany's defeat in World War II, the town once again became part of Poland, and its German population was expelled in accordance to the Potsdam Agreement.

It was demoted as a borough (gmina) centre in Międzyrzecz county of Gorzow Wielkopolski Voivodeship between 1975 and 1999.