This chapter details four case studies addressing the grid integration of wave and tidal current energy. The first three studies focus on the power quality issues arising from the connection of a tidal device or of a wave farm on their local network. More specifically, the first study investigates the impact of the SeaGen tidal turbine connected at Strangford Lough, Northern Ireland. The two other studies focus on the grid impact of a medium-size wave farm on its local network. The last study addresses the challenges in terms of grid integration at a power system level and details the capacity value of wave energy in Ireland.