Following the case study research strategy, this thesis has investigated the implementation of corporate environmental policies in subsidiaries of transnational corporations in Brazil. More specifically, it investigated six subsidiaries from three countries of origin - the United Kingdom, the United States and Germany - operating in the chemical and pharmaceutical sectors. This comparative study has resulted in a theoretical framework to explain transnational corporations' environmental practices. This framework follows an interdisciplinary approach, consisting of four levels. First, at the international level, an overview of the constraints regarding transnational corporations and environmental issues is addressed. The second level is represented by the environmental regulatory policies in the home and host countries. The third level accessed the influences from the industry's structure (in both international and Brazilian contexts). Finally, the fourth level is centred on the companies, which specifically discusses the home-host dilemma in the management of transnational corporations. The most important conclusion is that the main source of pressure over subsidiaries' practices is the environmental regulation of the host country. Nevertheless, there are cases of non-compliance and cases of overcompliance regarding Brazilian environmental legislation. However, these contradictory results are explained by the headquarters-subsidiary relationship. That is, poor environmental performance was explained by lack of control from the headquarters. Otherwise, good performance was explained by tight control from headquarters over subsidiaries' practices in Brazil. Additionally, there is indication that regulation is the main driving force in the home countries. However, attempts at self-regulation are in progress in the chemical industry in order to balance these external pressures for environmental improvements. Finally, there is evidence that the nationality of the selected companies is a relevant aspect of their environmental policies and practices. This is mainly because the legal requirements and management approach of the home countries are incorporated into their environmental management.