This thesis argues that democratisation affected environmental governance in Indonesia in two aspects: the development of environmental NGOs (ENGOs) and their involvement in policy networks. The former is analysed from three perspectives of social movement theories: `political opportunities', `framing' and `resource mobilisation'. The perspectives on the latter are derived from theories of the policy process: the `policy network' and Kingdon's `multiple streams'. Indonesian ENGOs developed significantly after the late 1980s, together with the democratisation movement. Democratic ideas `re-framed' environmental issues, which stimulated and politicised ENGO activities, while increasing `political opportunities' by shifting the values of government officials. They also enhanced ENGOs' accountability and their embedding in local communities. The democratisation of formal institutions after the late 1990s facilitated ENGO activities, but it was not the decisive factor for their development. Neither was economic growth: the impacts of economic changes were not straightforward. The case studies of the pulp-rayon company Indorayon and the policy-making process of participatory forestry in Wonosobo District show that the spread of democratic ideas resulted in the incorporation of ENGOs in policy networks, which had previously been a `politico-business oligarchy' in the authoritarian Suharto period, by increasing their resources, particularly `legitimacy'. Also, ENGOs significantly facilitated the inclusion of other actors in the networks. On the other hand, conventional informal institutions still remained and they constrained actors. This helped conventionally strong actors (e. g. the state and large businesses) to preserve their political leverage. The spread of democratic ideas influenced agenda-setting and policy formulation. It is suggested that utilitarian arguments for democratisation (i. e. democratisation for better ecological consequences) could produce policies that neglected the social aspect of sustainable development, which in turn negatively influenced their ecological and economic impacts. `Rights-based' arguments (e. g. participation is a right) seem more conducive to the efforts for sustainable development in the South.