The Resource Management Act (RMA) 1991 is a much discussed and frequently criticised piece of legislation in New Zealand. The RMA 1991 is much discussed because it is part of a substantial reform of New Zealand's resource management law. It is much criticised because the overall purpose of the RMA 1991 is to promote the sustainable management of natural and physical resources (S.5(1)) but the meaning given to sustainable management in the RMA 1991 (S.5(2)) is ambiguous. These discussions and criticisms focus on the legislation. Little research on promoting sustainable management in the context of resource management practice has been undertaken so far. This research needs to be done because the context of resource management issues and the public planning process will influence how sustainable management is interpreted and applied in resource management practice. This thesis is a comparative analysis of promoting sustainable management in four local government resource management issues: the northern access road issue, Christchurch; underground coal mining at Mount Davy, Rewanui; subdivision of Travis Swamp and Kennedy's Bush Spur, Christchurch; and air access into Westland National Park. The aims of the research are to establish: how sustainable management is being promoted in resource management practice; how important the RMA 1991 and promoting sustainable management is in determining resource management outcomes in the public planning process; and whether promoting sustainable management is resulting in a radical change in resource management practice. The thesis makes three conclusions. Firstly, that while sustainable management is an ambiguous concept a 'working' interpretation is emerging in resource management practice based on managing adverse environmental effects. Secondly, that the RMA 1991 and promoting sustainable management is important to legitimise resource management proposals in terms of the law, but it is not the raison d'etre for these proposals. Thirdly, that promoting sustainable management has resulted in changes in the way in which resource management proposals are assessed, but there are a lot of conitunities in resource management practice despite resource management law reform.