The National Marine Park of Alonnisos Northern Sporades was founded in Greece by Presidential Decree on May 16, 1992. It was the first of its kind in the country, and is currently the largest marine protected area in Europe. Besides the sea area, the park includes the island of Alonnisos, six smaller islands, as well as 22 uninhabited islets and rocky outcrops. It is located in the region of the Northern Sporades Islands, in the northern Aegean Sea. There is one other marine park in Greece, namely Zakynthos Marine Park.

Alonnisos, also transliterated as Alonissos, is a Greek island in the Aegean Sea. After Skiathos and Skopelos it is the third member of the Northern Sporades. It is 3 km (2 mi) (2 nm) east of the island of Skopelos. Alonnisos is also the name of a village on the island, as well as the municipality that encompasses the island and the village.