This paper presents the application of adaptive PI control design to a point absorber - wave energy converter (WEC) under force and motion constraints. Adaptive PI control has several features that make it attractive for WEC system. In particular, it has a clear physical interpretation. The “P” component converts the wave energy into useful energy, while the “I” component changes the WEC system natural frequency allowing the absorber to be more in phase with the incoming waves. However, standard adaptive PI control schemes in the literature do not have the ability to incorporate the constraints in the design phase. The main objective of this paper is to fill this gap by proposing a new adaptive PI control law that can take the constraints into account. Simulation results show that the new control law can improve the performance while respecting system limitations.