The signing of Agenda 21 by the UK government committed local authorities in England to drawing up local action plans for sustainable development in partnership with their citizens. This Local Agenda 21 (LA21) initiative appeared to provide the opportunity for radical changes in the trajectory of development and in the nature of local governance. This research set out to explain why this did not take place and what happened instead. It investigated how the nature of public involvement in LA21 was shaped by the local authority policy making processes through which it was developed, based on the premise that these involved the working out of the ambiguous and contested concepts of public involvement and sustainable development in a complex policy and institutional environment. Two contrasting LA21 processes were studied in detail, primarily through interviews with key policy actors, supplemented by observation and documentary evidence. The research showed that public involvement in LA21 was the outcome of contestation between actors with differing interpretations of the key concepts, who also had a range of other policy and institutional goals which affected their attitudes towards the initiative. Outcomes were determined by which interpretations were present and the ability of actors to control policy making processes to promote their goals. This explains both the variation within the LA21 initiative as a whole and the absence of 'radical' impacts: such goals were simply not present or they were suppressed by more powerful actors. The thesis develops more practically adequate characterisations of both sustainable development and public involvement. It also challenges Agenda 21's concept of a consensual participative planning process for sustainable development. It concludes by suggesting that policy making for sustainable development is inherently conflictive, and that public involvement in it is both a tool for policy makers and a channel for democratic input into policy making.