It is located in the middle of the island chain of the East Frisian Islands (Ostfriesische Inseln) and is the second smallest (smallest according to some sources) permanently-inhabited island in the chain. It is situated between Norderney (west) and Langeoog (east). There are two villages on the island - Ostdorf and Westdorf, although they have essentially merged into one. From the small port near the village of Neßmersiel (municipality Dornum) the ferry shippes to Baltrum.
The island has its own ferry terminal and a small airstrip. The island is about 5 km long and 1.5 km wide. It covers an area of 6.5 km² and has a population of around 600 people, swelling to about 3,500 during the summer months due to tourism. Tourists (mainly from the Ruhr Area in North Rhine-Westphalia) travel to Baltrum to enjoy the countryside of the national park "wadden sea of Lower Saxony", the beach, and facilities like an indoor swimming pool filled with sea water or a miniature golf course.