International, large-scale conferences on environment and sustainable development have shaped the public face of the global environmental governance. United Nations-led Earth Summits in Stockholm, Johannesburg, and Rio constituted hotbeds for global agreements on biodiversity, climate, and sustainability goals. The demand for ensuring wide participation beyond governmental actors has grown with each global conference. Increasingly, civil society and large non-governmental organizations (NGOs) are participating with greater access, resources, and experience. This chapter examines the influence of large environmental NGOs on key environmental conferences. It further compares the influence exerting strategies in context of ideology and organizational structure of the examined NGOs. The definition power or the ability of the global civil society to shape new environmental issues has changed since the Earth Summit in 1992. At the same time, alongside protest, cooperation, and coalitions have become popular instruments of large environmental NGOs to influence governmental actors and achieve favourable outcomes.