Tropical estuaries are often subject to very heavy human usage, and the variety of uses often leads to conflicts of interest. Their high fisheries productivity ensures that man is now very much part of the ecology of tropical estuaries. Although the major threats to estuarine fishes are usually linked to environmental degradation, there is also evidence to suggest that many fish species in tropical estuaries, particularly in south and southeast Asia, are declining in abundance primarily as a result of overfishing. Developed countries accord great importance to the conservation of ecosystems for their heritage value and in order to preserve fauna and flora, but in the developing world, the importance of estuaries for fisheries production and food security may seem at odds with arguments for their conservation. However, unlike many other human activities in and around estuaries, fisheries are almost completely dependent on the maintenance of ecosystem integrity. Both fisheries and conservation require sustainability as an outcome of management. Notwithstanding environmental problems, management therefore necessitates balancing the demands of fisheries and conservation. Examples show that this is possible, but there is little doubt that attempts to conserve estuaries in the tropics that do not take into account human activities are doomed to failure. The sustainable use of estuaries has, in some cases, become an integral part of the ecology of those systems, and fisheries form important criteria for designation of estuaries as internationally important under the RAMSAR convention.