Mussau Island
[Image:St Matthias Islands (Landsat).JPG|thumb|Mussau Island seen from space]
Mussau Island is the largest island of St Matthias Islands, Papua New Guinea, at. It is part of the New Ireland Province of Papua New Guinea. The island is a noted biodiversity hotspot with pristine primeval rainforest covering most of Mussau's hilly landscape. The island has over 243 endemic plant species as well as at least 47 native butterfly species.