One of the clearest messages to emerge from the wealth of environmental literaturethat has been generated since the late 1960s is that environmental degradationdoes not respect jurisdictional borders. Although many intemational and intrastateborders lie along geographical 'divides' such as mountain ridges and rivers, thesenatural features do not break physical and biological linkages of ecosystems.These linkages are often more pronounced where human-selected borders bisectespecially fluid environments, such as the ocean in which there is constantmovement of water, energy and marine life. Transboundary environmentalproblems are generally the result of planned human activities. They may becaused by specific development projects within one State or by activities in areasbeyond national jurisdiction (ABNJ), such as the high seas. Environmental impactassessment (EIA) has largely proven to be a successful tool for understandingand minimizing the environmental impacts of specific development projects oractivities since it was adopted in numerous States from the early 1970s. There isextensive, worldwide, experience in conducting EIAs for large scale land-basedprojects. However, the application of EIA to developments and activities in themarine environment is of more recent origin and often more challenging becauseof the large geographical and temporal scale of potential environmental impacts,as well as the increased likelihood that environmental harm might be caused toneighbouring States. Degradation of marine environments also tends to be moredifficult to monitor than terrestrial environments and ecosystems.