Schiermonnikoog (Dutch: [ˌsxiːrmɔnəkˈoːx] (listen); West Frisian: Skiermûntseach) is an island, a municipality and national park in the Northern Netherlands. Schiermonnikoog is one of the West Frisian Islands, and is part of the province of Friesland. It is situated between the islands of Ameland and Rottumerplaat.

The island is 16 km (9.9 mi) long and 4 km (2.5 mi) wide and is the site of the Netherlands' first national park. The only village on the island is also called Schiermonnikoog. Around 943 people permanently reside on the island, making the municipality both the least populated and the least densely populated in the Netherlands. Because the island is small and flat, only 200 islanders have taken out the special licence allowing them to keep their own car, with the result that the few streets are virtually car-free.

Roughly 300,000 people visit the island every year, staying in the 5,500 beds available in holiday homes, apartments and hotels. Most visitors, however, are day trippers (about 4,000 a day in July and August alone), with the result that after the last ferry leaves at 7.30pm, calm returns to Langestreek, the village high street.