The Mutant Underground is a network of informants, spies, and operatives who aid Xavier in overseeing mutants and mutant rights activities around the world. They draw their information from every news source available - newswires, internet postings, medical journals and tabloids, and that they also have friends in government agencies who risk a great deal by providing them with classified documents. Their computer system also has asub rosa link to the SHIELD. It is a secret network, but some of the various members were identified. Known affiliates include Carter St. Croix, Renee Majcomb, Sabra, as well as Mystique, Shortpack, Prudence, Jesse Bedlam, and Forge.
There appeared to be different branches of the Underground such as the Montana branch. It was apparently run by Nicole Lomenzo, Dr Derek Parsons, Lucas Wyndham. Parsons is a noted neurologists, Lomenzo a former Naval Officer, and Wyndham an astronaut. Their mutant abilities, however, were unknown.
Other branches are unknown at this time.