Puffin Island is the ninth largest island off the coast of Wales and marks the north-eastern end of the Menai Strait.

Puffin Island’s highest point is Carboniferous limestone, at 58m above sea level having steep cliffs on all sides. It has an area of 0.28 square kilometres (69 acres). The island is privately owned.

The island is a Special Protection Area (SPA), particularly because of its great cormorant colony of over 750 pairs, making it one of the largest colonies in the British Isles. It also has good numbers of guillemot, razorbill, cormorant ("shag") and kittiwake nesting, and in recent years, small numbers of common eider and black guillemot.