Background: Mycoplasma genitalium can cause nongonococcal urethritis in men and is associated with cervicitis and pelvic inflammatory disease in women. public health concern; however, surveillance remains limited. Following successful pilots in 2019 and 2020, the UK Health Security Agency (UKHSA) has developed a protocol for routine national sentinel surveillance of AMR in M. genitalium in England (MARS). Methods: The MARS protocol aimed to estimate the prevalence of macrolide and fluoroquinolone resistance in M. genitalium infections among adults (≥18 years) attending sentinel sexual health services (SHSs) in England, and characterise factors associated with resistance. Sample size calculations were performed. National STI surveillance data was used to analyse reported M. genitalium diagnoses from January to June 2022. Recruitment for MARS prioritised high-reporting SHSs representing a wide geographic distribution. The UKHSA has developed molecular assays, amplifying and sequencing the 23S rRNA gene (region V) and the quinolone resistancedetermining regions of the parC and gyrA genes for the identification of macrolide and predicted fluoroquinolone resistance in M. genitalium, respectively. All M. genitalium specimens will have molecular resistance testing performed and additional demographic, behavioural and clinical information will be provided by the SHSs. Results: MARS will collect consecutive M. genitalium-positive clinical specimens (urine, urethral swabs, cervical swabs, vaginal swabs, rectal swabs) from routine patient care at participating SHSs, during a 4-month period in 2023. A sample size of 1,000 specimens is required to identify whether the proportion of individuals with macrolide and/or predicted fluoroquinolone resistant M. genitalium infections differed from the national pilot study estimates, with a power of 90% and 5% significance level. As of 3 January 2023, 23 SHSs had been recruited within 5 of the 9 UKHSA regions, accounting for 41.5% (n=1,235/2,978) of diagnoses reported nationally. Resistance will be stratified by key enhanced variables, such as age, ethnicity, and HIV status, to characterise factors associated with resistance. Conclusions: We report the initiation of routine surveillance of AMR in M. genitalium through a sentinel network of SHSs in England, aiming to inform national clinical management guidelines and contribute to the global understanding of emerging resistance. [ABSTRACT FROM AUTHOR]