Osmussaar is the most in quarter north-west situates island in Estonia, it situates in a mouth of Gulf of Finland ca 10 km from mainland. The surface of the island is 480 ha, length 4,6 km, width 1,3 km and the length of coastline is 14 km.

Osmussaare Landscape Reserve was formed  in 1996 and the main goal of this protection area is to protect and preserve the values of geology and landscape. The administrator of the landscape reserve is Silma Nature Reserve Administration. The management plan (2004-2008) to preserve natural values of this island was fixed in 2005.

From Habitat Directive’s 92/43/EEC I appendix following habitat types appear on Osmussaare island: coastal lagoons (1150), Annual vegetation of drift banks (1210), Perennial vegetation of stony banks (1220), Vegetated sea cliffs of the Atlantic and Baltic coasts (1230), Boreal Baltic coastal meadows (1630), Juniperus communis formations on heaths or calcareous grasslands (5130), Semi-natural dry grasslands and scrubland facies on calcareous substrates (Festuco-Brometalia) (6210), Nordic alvars and Precambrian

calcareous flatrocks (6280), Molinia meadows on calcareous, peaty or clayey-silt-laden soils (Molinia caeruleae) (6410), Alkaline fens (7230) and Fennoscandian hemiboreal natural old broad-leaved deciduoud forests (Quercus, Tilia, Acer, Fraxinus or Ulmus) rich with epiphytes (9020). One vascular plant from Habitats Directive’s I appendix that grows on Osmussaar is Liparis loeselii. From Bird Directive I appendix on the island nests Circus aeruginosus, Tetrao tetrix, Crex crex, Grus grus, Calidris alpina, Sterna hirundo, S. paradiseae, Sylvia nisoria and Lanius collurio.