Deposition of reactive nitrogen from anthropogenic sources greatly exceeds natural fluxes and, in Scotland, a large proportion of semi-natural ecosystems (i.e., communities of native species, modified to varying degrees by human activities) currently experience nitrogen deposition loads in excess of the thresholds at which adverse impacts have been reported. This review provides a summary of current knowledge on the thresholds for adverse nitrogen impacts in Scottish terrestrial semi-natural ecosystems, ecosystem responses to excess nitrogen deposition, the scope for mitigating the impacts of nitrogen deposition through habitat management and metrics which could be used to monitor ecosystem recovery.