One of the major sources of the greenhouse gas, methane, is ruminant digestion, which has been implicated in recent rises in atmospheric methane levels, due to increasing domestic animal populations. However, most current estimates of emissions from cattle and sheep are based on measurements taken under controlled conditions and do not take into account the different types of gaseous exchange which can occur between components of the environment. This study will aim to define methane exchanges between grazed grasslands, their soils and the atmosphere, using field-based measurements. Net methane fluxes will be quantified from grassland grazed under different conditions, including extensive, intensive, cattle, sheep, rotational and continuous grazing systems. Rates of emission and deposition of methane to and from grassland soils will be determined and the influence of environmental factors such as wind, temperature and moisture will be investigated. The results of the study will be used to compile a methane emission inventory for UK grasslands at systems, regional and national levels. The research is expected to provide information which will be relevant to other temperate grassland areas, and may be used to predict the behaviour of methane in the soils of other agricultural and natural ecosystems.