Case studies are used to compare the use of strategic environmental assessment (SEA) Scotland and New Zealand by applying the Glasson-Gosling typology of SEA practice. The results suggest SEA's effectiveness in promoting sustain-ability is determined by its capacity to shape the decision-making processes governing all aspects of spatial development. New Zealand's Resource Management Act confines SEA to evaluating environmental aspects of territorial land-use and resource-management plans. Without efforts to integrate SEA into new community planning powers under the 2002 Local Government Act, this will limit its use in supporting broader sus-tainability objectives. Scotland's recent Environmental Assessment Act embraces all public-sector policies, plans and programmes, offering SEA more scope for influencing policy formulation and the delivery of sustainable development.