Sassnitz (German pronunciation: [ˈzasnɪts] ^ⓘ, before 1993 in German: Saßnitz) is a town on the Jasmund peninsula, Rügen Island, in the state of Mecklenburg-Vorpommern, Germany. The population as of 2012 was 9,498.

Sassnitz is a well-known seaside resort and port town, and is a gateway to the nearby Jasmund National Park with its unique chalk cliffs. The decommissioned British submarine HMS Otus was purchased by a German entrepreneur and towed to Sassnitz to be a floating museum. The Sassnitz area is most popular for its famous chalk rocks (Kreidefelsen), which inspired artists like Caspar David Friedrich.

The borough of Sassnitz lies in the northeastern part of the island of Rügen, covering the eastern part of the Jasmund peninsula as far as the sand bar of Schmale Heide to the south. The countryside there is renowned especially for its chalk cliffs. In addition, ice age depositions dominate the landscape. Its depressions have frequently been filled by small lakes. The most striking chalk cliff is the 118-metre (387 ft)-high Königsstuhl. Large parts of the borough are covered by various types of trees with their typical habitats. One feature is the forest on the coastal slopes. Here there are rare trees like wild pear, wild apple, and yew. The town lies on the coastal slopes at the southern end of the Stubnitz, a 7.5-kilometre (4.7 mi)-long and up to 4-kilometre (2.5 mi)-wide beech forest. The remaining land areas consist of moors, beach, meadows, pastureland, and settlements. In the south of the borough, near Mukran, are the Wostevitz ponds, a boggy depression that is protected as a nature reserve. The small stream of Steinbach flows through the built-up area of the town.

Near the Königsstuhl lies another lake, the Herthasee, which has a diameter of about 150 metres (490 ft) and is up to 11 metres (36 ft) deep.

The borough of Sassnitz is divided into the following municipalities: Blieschow, Buddenhagen, Dargast, Drosevitz, Dubnitz, Klementelvitz, Mukran, Neu Mukran, Rusewase, Sassnitz, Staphel, Stubbenkammer, Werder, and Wostevitz.

The original landscape on the Jasmund is geologically very young. Its formation began with the end of the Weichselian glaciation about 12,000 years ago, when the ice sheet left behind there a Young Moraine landscape. As a result of thawing inland ice the underlying land and rose and hollows were filled with water. The predecessor to what later became the Baltic Sea, the Ancylus Lake, was formed.

Next, a cold steppe spread across the region. Later, birch and pine forests emerged, followed by oak forests. During the last 1,000 years, beech forests dominated the area. Lakes formed in the endorheic depressions, some of which silted up and became bogs. About 6,000 years ago, the sea level rose to its present level, leaving upland areas to form the Jasmund. As a result of the erosive action of waves and currents created, steep shores were formed that still characterise the landscape.

It was not until 1906 that the farming and fishing village of Crampas and the fishing village of Sassnitz were merged into the municipality of Sassnitz. Fishing was (and is) important. The desire of many city dwellers to relax by the sea led, at the end of the 19th century, to a rapid and strong growth on the shores of the Baltic and North Sea, as well as on Rügen itself. As early as 1824, it is recorded that the family of the Berlin theologian Friedrich Schleiermacher went on a beach holiday to Sassnitz.