'Sustainable use' of wildlife resources and 'community based conservation' are two themes recurrent in contemporary statements of wildlife conservation policy, and their use is in response to a perceived 'deep conservation crisis' which has in part arisen from exclusionary and restrictive conservation practices. The extent to which the legal harvest of marine turtle eggs in Ostional, Costa Rica, is an example of sustainable use and community based conservation is evaluated in this paper. Field research using in-depth interviewing and a household questionnaire was undertaken in Ostional during 1994 and 1995, to investigate local perceptions of the egg harvesting project, both positive and negative. Socio-economic benefits from, and legal and administrative structures supporting, the project were found to be fundamental to community support for a limited egg harvest and allowed for community participation in, and control of, resource use. Participation and control were key to local support for conservation of nesting marine turtles and their eggs. Attempts to use wildlife sustainably must be considered on a case by case basis, to account for the biological nature of the wildlife resource and environment in question and for local socio-economic, political and historical conditions. Nevertheless, some of the lessons learned from the attempt to implement sustainable use and community based conservation in Ostional may be more widely generalized, and may help inform other efforts to reconcile wildlife conservation objectives with local development needs.