The island of El Hierro (Spain), a UNESCO Biosphere Reserve in the Atlantic Ocean, aims to become the first 100% renewable energy island in the world. With a €54 million wind project already under way, the present research looks at the island’s wave resource using a 44-year hindcast dataset obtained through numerical modelling. The geographical distribution of wave energy is examined on the basis of eight study sites around the island. A substantial resource is found west and north of El Hierro, with average wave power in the order of 25 kW m−1 and total annual energy in excess 200 MW h m−1; the resource is less abundant east and south of the island. In addition to these geographical variations, wave energy in El Hierro presents seasonal variations, with energetic winters and mild summers. After analysing the total resource and its spatial and seasonal variations, its composition in terms of sea states (significant wave heights and energy periods) is examined, and how this composition affects the selection of the Wave Energy Converters to be installed is discussed.