The ensemble numerical prediction of ocean waves is considered and all published works on this new topic in Geosciences are reviewed. A Wave Ensemble Prediction System is described where a global third-generation wave model is adopted. Twenty members are generated by a method based on Empirical Orthogonal Functions and a particular realistic case where several extreme wave events occurred is analysed.The ensemble numerical prediction of ocean waves is considered and all published works on this new topic in Geosciences are reviewed. A Wave Ensemble Prediction System is described where a global third-generation wave model is adopted. Twenty members are generated by a method based on Empirical Orthogonal Functions and a particular realistic case where several extreme wave events occurred is analysed.