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The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations^{, , –}. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere^,, which—given methane’s lifetime of several centuries—predicts an even, well mixed distribution of methane^,,. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of …