AbstractA broad range of chemical contaminants and pollutants have been measured within the Chagos Archipelago. Contamination is amongst the lowest in the world. Whilst much data is in the open literature, the chapter also includes details of extensive pollution monitoring for the atoll Diego Garcia which hosts a military facility. Hydrocarbons present are primarily of a natural origin with negligible evidence of contamination from petroleum or combustion origins. Tar balls, however, have been reported on several beaches in the Archipelago. Analyses of faecal steroids provide negligible evidence of sewage contamination. ‘Persistent organic pollutants’ (POPs), including PCBs and pesticides, were generally below analytical detection limits, as were polyfluorinated compounds, brominated, chlorinated and organo-phosphorous flame retardants, fluorinated tensides, and surfactants (PFOS). Antifouling biocides and herbicides in Diego Garcia show negligible contamination. Metal concentrations are very low. Levels of most contaminants are typically comparable to those recorded in environments perceived to be pristine, for example, the Antarctic. In Diego Garcia, extensive monitoring includes regular analyses in accredited US laboratories of over one hundred metals and organic contaminants. Results generally reveal concentrations below detection limits. This is in agreement with the open literature surveys. These legislated assessments are designed to ensure both environmental and human health preservation. Whilst many detection limits are higher than those of the independent surveys, they generally confirm the pristine nature of the Archipelago. Beach surveys, however, revealed a surprisingly high number of pieces of debris throughout the Archipelago, mainly plastics of South East Asian origin. The number of litter pieces in Diego Garcia was less than in the other atolls, reductions being attributed to beach clean-up events. Microplastic contamination is shown to be both widespread and relatively high compared to other locations on a global scale, and there were significantly more microplastics at uninhabited atolls compared to the Diego Garcia, showing the potential for microplastics to accumulate in remote locations. Holothurian (sea cucumber) poaching has been another significant environmental pressure on the coral reefs of Chagos and is included in this review, in view of the reported ecological benefits of the group to reef health and resilience.