Environmental taxes are relatively new instruments and are likely to constitute an essential part of countries' efforts to avoid environmental degradation. This work analyses the extent to which various categories of environmental taxes may be inconsistent with the non-discrimination provisions of the General Agreement on Tariffs and Trade 1994, and how such conflicts can be resolved within the existing rules. As non-discrimination obligations are fundamental rules in the multilateral trading system, such potential conflicts are of great importance both to the régime for the liberalisation of international trade and to environmental protection measures. The author provides a detailed analysis of the role and nature of environmental taxes, and assesses to what extent the relevant provisions of GATT 1994 may impede the use of these taxes, in light of the non-discrimination provisions, the general exceptions and the rules concerning nullification or impairment of benefits. The work also examines in general terms the possibilities of eliminating potential conflicts between environmental measures and the provisions of GATT 1994. Table of Contents: Part I - Introduction - 1. Introduction: 2. Environmental Problems and Strategies to Deal with Them - The Role of Environmental Taxes; 3. Introduction to Relevant Rules and Principles of GATT/WTO. Part II - Internal Taxes - 4 General Introduction; 5. The Scope of Article III; 6. Product-Similarity Clauses; 7. Domestic and Foreign Products are Subject to Separate Tax Arrangements - Explicit Discrimination; 8 Domestic and Foreign Products are Subject to the Same Tax Arrangement - Implicit Discrimination. Part III - General Exceptions - 9. General Issues; 10. Policy Purposes Covered by Article XX; 11. Requirements Concerning the Relationship between the Contested Measure and its Purpose; 12. The Preamble to Article XX. Part IV - Nu