Racomitrium heath, a moss-dominated mountain summit community, is one of the most extensive remaining near-natural habitats in the UK, contributing considerably to biodiversity.  Degradation of this internationally important habitat has been attributed to two anthropogenic factors, atmospheric nitrogen pollution and high sheep grazing pressures. This study makes a valuable contribution to our knowledge of current Racomitrium heath condition.  An extensive survey of heaths throughout the UK and also in Iceland, Norway and the Faroes, revealed the importance of the Scottish Highlands as a core location of optimal development within the habitat’s European distribution.  Considerable progress has been made in identifying the environmental drivers that influence current heath condition, and an updated model is presented, which provides an improved understanding of the mechanisms responsible for its decline. While climatic conditions were revealed as the most influential driver of community composition, nitrogen deposition was a more important driver of the performance of R. lanuginosum, the dominant species within the community.  Contrary to previous studies, high nitrogen deposition rates were found to have a fertilising effect on this key moss species, stimulating growth. However, it can now be proposed that declines in R. lanuginosum abundance are attributable to nitrogen-enhanced shoot decomposition, causing reduced moss mat depth.  Higher temperatures and grazing pressure were found to exacerbate the impacts of nitrogen deposition, leading to increased nutrient availability, shifts in community composition and loss of habitat. The study also provided evidence to suggest that, despite their long-term impacts, Racomitrium heath has the potential to recover from nitrogen pollution and high grazing pressures.  However, global warming is likely to present an additional and significant threat to this internationally important habitat in the future.