Today it is widely recognised that international investment activities can bring significant economic benefits for host countries. To promote a favourable investment climate, international organisations were set up to facilitate the settlement of foreign investment disputes, or to provide financial insurance for investors against non-commercial risks. Moreover, international financial institutions offer finance for governments or private enterprises to implement investment projects. States have also concluded international investment agreements to provide guarantees on the treatment and protection of foreign investors. Meanwhile, however, these investment activities can also create environmental problems for host countries and lead to human suffering. As states have been generally reluctant to take the initiative to secure effective implementation of environmental rules at the international level, allowing entities other than states to make environmental claims before international dispute settlement mechanisms offers practical approaches to protecting community interests and ensuring the fulfillment of international environmental standards in the course of international investment activities. This thesis considers the extent to which civil society organisations (CSOs) can promote, and have indeed promoted, environmental considerations in settling investment-related environmental claims through alternative means of dispute resolution on the international plane. It explores how CSOs have brought environmental perspectives in response to adverse impacts arising from investment activities. It also evaluates the implications of their claims for resolving relevant environmental issues and promoting compliance with international environmental standards during investment activities.