This study investigates factors influencing farmers' motivations for participation in the Cambrian Mountains ESA scheme (Wales, U.K.). Emphasis is placed on analysing whether significant correlations exist between ESA participation and specific factors. A behavioural approach is used for analysis, largely based on Brotherton's classification into ''scheme factors'' (e.g. payments) and ''farmer factors'' (e.g. age of farmer), but which expands this classification by including the ''information environment'' of a farmer and ''dynamics within the farm district''-variables which this study shares with some actor-network approaches. While size and existence of remnant wildlife habitats were strongly correlated with overall participation, payments offered by the scheme, information provided by ADAS, scheme flexibility, the ''successors factor'' and dynamics within the district were of particular importance for participation on farms of marginal ESA eligibility (i.e. small farms lacking substantial semi-natural habitats). Age, education and length of residency were important for explaining differential entering of specific habitats (especially broadleaved woodlands) into the ESA scheme, while scheme duration, dependence on the farm for income, tenure and the general information environment of the farmer did not influence overall participation. The paper concludes by arguing that a behavioural approach offers a valuable insight into farmers' decision-making behaviour with regard to participation in agri-environmental schemes, and that this study may be seen as a starting point that could be expanded through the use of related methodologies.