With considering the increasing of global temperature, and also the concern of global climate change, many policy makers worldwide have been accepted the importance of reducing greenhouse gas emissions, in particular from the power industries so the importance of the renewable energy is obvious. Wave energy is one of the renewable energy sources. And has the potential to play a valuable part in a sustainable energy future. Wave energy is also one of the predictable energy sources that depending on oscillating the surface of water. The wave energy system for generation electricity in the last few years has been growing rapidly. There are several methods that have been proposed to classify wave energy converters with considering working principle, location and size such as the oscillating water column (OWC), oscillating body systems, overtopping converters and etc. In almost every system, optimal wave energy absorption includes some kind of resonance, which implies that the geometry and size of the structure are linked to wavelength. The resonance allows to relatively small device to producing large power. This paper discusses about the various technology of wave energy converters.