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Abstract The main factors affecting the abundance and composition of the invertebrate fauna in grassland are reviewed. Old grasslands with species-rich swards and complex structure support an abundant and diverse fauna compared with uniform leys with few species. Seasonal and successional changes in the sward are accompanied by equally marked changes in the invertebrate community. Climate and weather have a major influence, but their effects may be modified locally by the availability of shelter. Soil physical and chemical characteristics influence the soil fauna directly and the above ground fauna indirectly through the vegetation. Food quality as determined by physical and chemical plant characteristics strongly influences invertebrate growth, reproduction and mortality. The main biotic factors affecting abundance are natural enemies and disease; these, in combination with weather and food quality, are often the main agents in determining population density in natural communities. Management practices such as grazing, cutting, fertilizer application, burning, soil water control and pesticide use profoundly influence the sward and induce correspondingly great changes in the invertebrate community.