X-Men: The 198 is a comic book limited series that was published by Marvel Comics and set in the Marvel Universe shortly after the House of M and Decimation events. The five-issue series began publication in January 2006.
The series focuses on the supporting cast of the X-Men, whose ranks have been severely depleted following Decimation.
In House of M #7, the Scarlet Witch removes the powers of the overwhelming majority of the world's mutants in an event that is eventually called "M-Day". As a reaction, the United States government forms a superhuman-monitoring Office of National Emergency (O*N*E), and sets up a team of human-piloted Sentinel robots (Sentinel Squad O*N*E) to monitor the Xavier Institute. X-Men: The 198 revolves around the tension and conflicts of the 198 mutant refugees on the Xavier Institute grounds and the Sentinel Squad O*N*E. Tensions also rise between the X-Men.
The 198 Files:
The 198 Files is a database maintained by O*N*E that attempts to classify and provide intelligence on the mutants whose powers remained after M-Day. The one-shot X-Men: The 198 Files is set in the style of a government dossier and sent to O*N*E's deputy director Valerie Cooper. It provides the classification of 134 of the 198 mutants supposedly unaffected by M-Day and was released in January 2006 as a counterpart to the five-part limited series The 198 which shows the conflict of the remaining mutants seeking refuge at the Xavier Institute, and the Sentinel Squad O*N*E.