Terezín is the name of a former military fortress and adjacent walled garrison town in the Ústí nad Labem Region of the Czech Republic.

In the late 18th century the Habsburg Monarchy erected the fortress, as well as a large walled town directly across the Ohře River, near its confluence with the Elbe River, and named it after Empress Maria Theresa.

During WWII, the Gestapo used Terezín, better known by the German name Theresienstadt, as a ghetto, concentrating Jews from Czechoslovakia, as well as many from Germany, Austria, the Netherlands, and Denmark. More than 150,000 Jews were sent there, and although it was not an extermination camp about 33,000 died in the ghetto itself, mostly because of the appalling conditions arising out of extreme population density. About 88,000 inhabitants were deported to Auschwitz and other extermination camps At the end of the war there were 17,247 survivors.

After the war, Theresienstadt was resurrected as Terezín, dropping the German "stadt" from its name but still retaining a military garrison. In 2002, the fortress, which was in a deteriorated condition, was listed in the 2002 World Monuments Watch by the World Monuments Fund.