GUTs also predict the existence of topological defects such as monopoles, cosmic strings, domain walls, and others. None have been observed and their absence is known as the monopole problem in cosmology.

Some common GUT groups are:

- SU(5), Georgi-Glashow model
- SO(10)
- SU(5)XXU(1), Flipped SU(5).
- SU(4)XXSU(2)XXSU(2), Pati-Salam model
- SU(3)XXSU(3)XXSU(3), Trinification
- E
_{6} - Technicolor models

As of 2004, there is still no hard evidence nature is described by a GUT theory. In fact, since the Higgs particle hasn't been discovered yet, it's not even certain if the Standard Model is fully accurate.