Alonnisos is a Greek island situated in the Aegean Sea, positioned east of mainland Greece and Magnesia, northeast of Euboea, and northwest of Skyros. It forms the third member of the Northern Sporades archipelago, located just three kilometers east of Skopelos. The municipality encompasses the main island along with several smaller nearby islands, including Adelfoi, Gioura, Kyra Panagia, Peristera, Piperi, Psathoura, and Skantzoura.