The Gulf of Nicoya is a tectonic estuary on the Pacific coast of Costa Rica (10°N–85°W), extending about 100 km from the Tempisque river to the 500 m isobath. A dry season (December–April) and a rainy season (May–November) exert a significant impact on its water characteristics. The estuary is the most important fishing ground of Costa Rica, and the main Pacific ports are located within it. Coastal zone development has increased in recent years. In 1979 a research programme to study the Gulf was established at the University of Costa Rica, and foreign scientists were invited to work jointly with local experts to achieve the goals of the evaluation. More than 80 papers have been published to date, making the Gulf one of the best known tropical estuaries. The study of soft-bottom communities is an important component of this research programme. Past benthic research focused on the description of the structure of communities, while future efforts will find an unexplored field in the study of energy flow and community interactions. More than 200 species of fish, and 400 of benthic invertebrates have been identified. Future cooperative research is most welcome in larval ecology, interactions between size groups, and physiological tolerances. Considerable experience has been accumulated in the experimental manipulation of soft-bottom communities of high latitudes. This branch of ecology, however, remains little explored in the tropics. Future cooperative efforts in the Gulf of Nicoya will be established on solid ground, formed by a data base that has been improved since 1979, the existence of a marine research centre and a group of active, local scientists who have experience in working together with foreign expertise.