The causes of variation in effectiveness of environmental public policy are subject to debate.  Different levels of effectiveness in wider government policy are commonly explained by external influences. Fewer studies focus on the role of factors within the Executive, such as institutional arrangements, differing levels of capability in policy-makers, and ways ideas shape how people and institutions perceive environmental values and issues. This study aims to advance our understanding of how such factors combine to effect environmental policy in a specific national jurisdiction. The research investigates how environmental policy efforts of environmental government departments are influenced by factors within the Executive in New Zealand, and how these factors contribute to variability in environmental policy effectiveness.

Drawing on theories about the main drivers of policy change and ideas about environmental policy effectiveness, the thesis puts forward a framework to analyse three case studies of environmental policy development between the 1990s and the late 2000s: oceans policy; biodiversity policy; and water policy.

The main finding of the research is that four key intra-government variables are the primary determinants of environmental policy effectiveness in New Zealand. These are: the level of government commitment to environmental values relative to other values; the environmental commitment and capability of ministers holding environmental portfolios; the capability of officials within the environmental departments, notably their ability to provide leadership; and the extent to which environmental departments are organised and equipped to play a lead role in the development of environmental policy. These four variables are interdependent. Government will and the actions of ministers and officials can enable structural change that facilitates environmental organisations to take a leadership role, but where institutions do not allow or facilitate this to happen, environmental policy can be constrained or ineffective even where there is government commitment.  
From an organisational perspective features that stand out as being most important to enhance environmental policy effectiveness are: ensuring that priority is placed on environmental imperatives in policy design; concentrating effort by reorganising and aligning operating procedures internally in a timely way to focus on the issue at hand; forming close alliances with supportive departments and drawing in opposing departments; and organising to shape and lead the policy process within the machinery of government