Satellite altimetry gives a new perspective on ocean wave climate. Measurements around the British Isles show a strong seasonality, with exceptionally large average wave heights to the west and north of the British Isles in the winter. Furthermore, the interannual variability of winter wave climate is very high. Most of this variability can be described by a strong linear dependence on the North Atlantic Oscillation (NAO) index. This relationship may largely explain observations of increasing wave heights in the northeastern Atlantic and northern North Sea during the latter decades of the 20th century, coincident with a long-term rise in the NAO.