Gauge bosons carry fundamental forces. There are three known gauge bosons, which are elementary particles. For example, the photon carries the electromagnetic force. The three types of gauge bosons are: photons for electromagnetism, gluons (eight kinds) for strong force, and W and Z bosons (three kinds) for weak force. Other theoretical gauge bosons are predicted, such as gravitons for gravity. The Higgs boson is another fundamental particle of a type called a scalar boson.