The United Nations Office for Martian Affairs (UNOMA) was the international political body that dealt with all matters pertaining to human activities on Mars in the majority of the 21st century. UNOMA was answerable to the UNO General Assembly but progressively became a more independent entity as the influence of transnationals in political affairs increased.

UNOMA was created circa 2026 with the Ares mission of the First Hundred and worked in close association with NASA Mission Control and Baikonur, to whom the majority of the First Hundred answered to. In no small part thanks to the public efforts of Ann Clayborne, the initial stance of UNOMA was that human activities should have a minimum impact on the Martian environment, which was greatly challenged by Sax Russell. Things came to a head with the affair of the windmills, designed by Russell to be spread all over the planet and generate heat. After much debate, the UNOMA committee on environmental alterations approved of their dissemination in 2030. It was not long before the subcommittee on terraforming and the General Assembly approved a package of terraforming efforts, among them the distribution on the Martian surface of genetically engineered microorganisms.

In the decades that followed, UNOMA supported terraforming fully. UNOMA approved the launching of other colonies to Mars and acted as the emigration authority for all interplanetary travel. UNOMA assigned Russell as the scientific head of terraforming efforts and financed the creation of the terraforming headquarters at Echus Overlook. In the early 2040s the UNOMA headquarters were moved from Underhill to Burroughs, which triggered Burroughs' construction boom. German Helmut Bronski was the UNOMA top official at that time.

At that time, with Martian population increasing and the economic prospect of Mars-Terra trade was becoming closer to reality, it became evident that UNOMA's authority was being undermined by a consortium of transnationals. Security had been the purview of UNOMA, however more and more private security troops were called for and dispatched. UNOMA approved the space elevator project supported by Phyllis Boyle and awarded contracts to transnationals for its construction. Progressively UNOMA was participating in breaking the UN Mars Treaty along with the transnationals, and UNOMA positions on Mars were being filled by officials that had previously worked in transnationals. John Boone attempted to shed light on these happenings and was victim of harassment and a tentative to be framed for murder.

UNOMA and transnational interest were victims of sabotages orchestrated by Martian resistance groups that were organizing themselves and UNOMA had them investigated. The treaty renewal in 2057 under UNOMA supervision rearranged the terms in favor of private exploitation of Martian resources. Frank Chalmers attempted to temper the unrest that was rising and used UNOMA police to make arrests. However in 2061 a revolution violently broke out. UNOMA police and transnational security troops worked in tandem in crushing the revolutionary forces.

In the aftermath of the revolution, UNOMA gave way to a different organization, the UN Transitional Authority.