The invertebrate communities associated with intertidal mytilid mussel species were investigated on a variety of wave-exposed rocky shores around the coasts of the British Isles, Irish Republic (Mytilus edulis) and Chile, South America (Perumytilus purpuratus). A total of 192 different taxa were identified in Mytilus edulis beds at various rocky shore sites in the British Isles and Irish Republic, while 35 taxa were identified to higher taxonomic levels in Perumytilus purpuratus beds in Chile, South America. Significant small-scale spatial variations in community structure were observed at two locations in Wales, while significant large-scale spatial variations in community structure were observed within mussel beds both in the British Isles and Irish Republic and in Chile. Additionally, the communities associated with M. edulis and P. purpuratus differed significantly, when compared at the same taxonomic levels. The structure of the invertebrate communities associated with M. edulis populations showed significant intra-annual variation, while those associated with M. edulis and P. putpuratus displayed significant inter-annual variation. The spatial and temporal variation observed in the structure of the invertebrate communities associated with intertidal mussel beds were deemed to be the result of a variety of natural processes, along with stochastic events. Variation in measured environmental factors in the mussel beds did not fully account for the observed variation in community structure, although some factors, such as mussel density were shown to have some structuring effect. It is concluded that the structure of the invertebrate communities associated with intertidal mussel on rocky shores are highly variable, both spatially and temporally. However, a small subset of taxa often display the same multivariate patterns as the entire data set; a phenomenon which could be utilised in any monitoring or impact studies involving mussel communities.