Ratzeburg is a town in Schleswig-Holstein, Germany. It is surrounded by four lakes—the resulting isthmuses between the lakes form the access lanes to the town. Ratzeburg is the capital of the district Herzogtum Lauenburg.

The Prince-Bishopric of Ratzeburg was an ecclesiastical principality of the Holy Roman Empire that was located in what is today the states of Schleswig-Holstein and Mecklenburg-Vorpommern in Germany. It was established in 1236 and disestablished following the Peace of Westphalia in 1648. The state capital was the city of Ratzeburg. The Diocese of Ratzeburg had originally been established as a diocese of the Catholic Church in the 11th century but had fallen into abeyance; as a result of the Wendish Crusade, the diocese was re-created in the middle of the 12th century. The territory of the prince-bishopric was managed by secular lords on behalf of the Bishop of Ratzeburg. As a Prince-Bishopric of the Empire, the territory of the state was not identical with that of the bishopric, but was located within its boundaries and made up about a quarter of the diocesan area. When the Prince-Bishopric was disestablished, a new entity was established — the Principality of Ratzeburg. The principality became an exclave of the Duchy of Mecklenburg-Strelitz.