This thesis brings together two responses to the question ‘how can the law extend the timeframe for environmentally relevant decision-making?’ The first response is drawn from the context of institutional investment, and addresses the timeframe and breadth of environmental considerations in pension fund investment decision-making. The second response is related to the context of public environmental decision-making by legislators, the judiciary, and administrators. Three themes underlie and bind the thesis: the challenges to decision-making posed by the particular temporal and spatial characteristics of environmental problems, the existence and effects of short-termism in a variety of contexts, and the legal notion of the trust as a means for analysing and addressing problems of a long-term or intergenerational nature. These themes are borne out in each of the four substantive chapters. Chapter III sets out to demonstrate the theoretical potential of pension funds to drive the reduction of firms’ environmental impact, and, focusing particularly on the notion of fiduciary duty, explores the barriers that stand in their way. Chapter IV provides a practical application of the theoretical recommendations outlined in its predecessor. It provides a framework outlining how pension funds might implement a longer term, more sustainable approach to investing. The second half of the thesis, operating in the context of public environmental decision-making, is centred upon a particularly poignant legal notion with respect to the environment and time: the concept of intergenerational equity. Just as the first half of the thesis deals with the timeframes relevant to investment decision-making by pension funds within the bounds of fiduciary duty, largely a private law affair with public implications, the second half of the thesis is concerned with the principle of intergenerational equity as a means for extending the decision-making timeframe of legislative, judicial and administrative decision-makers. As previous analyses of the concept of intergenerational equity provide little insight into its practical implications when applied to particular factual situation, Chapter V sets out the structure of the principle of intergenerational equity as revealed by case law. Chapter VI brings together the issues from the first three papers by conceptualising intergenerational equity in resource management as an issue of long-term investment. Long-term environmental decision-making faces many obstacles. Individual behavioural biases, short-term financial incentive structures, the myopic pressures of the electoral cycle and the tendency of the common law to reinforce the (often shorttermist) status quo all present significant barriers to the capacity of both private and public decision-makers to act in ways that favour the longer term interests of the environment. Nonetheless, this thesis argues that there is reason for hope: drawing upon the three themes that underlie all of the substantive Chapters, it articulates potential legislative changes and recommends the adoption of particular governance structures to overcome barriers to long-term environmental decision-making.