In physics, the term X boson is used in various different contexts.

In particle physics, an X boson is usually a new elementary particle analogous to the W boson and Z boson, but one that corresponds to a new type of force, such as the forces predicted by grand unified theory. The interactions arising due to these X bosons are responsible for new phenomena such as the proton decay. A related type of new particles is called Y boson .

In condensed matter physics, the term "X boson" has a different meaning.