I review and extend three approaches to trade and environmental policies: competitive general equilibrium, oligopoly and monopolistic competition. The first two have surprisingly similar implications: deviations from first-best rules are justified only by constraints on policy choice (which motivates what I call a "single dividend" approach to environmental policy), and taxes and emissions standards differ in ways which reflect the Le Chatelier principle. I also show how environmental taxes may lead to a catastrophic relocation of industry in the presence of agglomeration effects, although not necessarily if there is a continuum of industries which differ in pollution intensity. My objective in this paper is to review and extend some points of intersection between international trade theory and environmental economics. These two sub-fields of economics have much in common. At the theoretical level, both are branches of applied microeconomics, focusing on the implications of a set of important real-world phenomena:differential international mobility (of goods, factors or ideas) in the case of trade theory, specific externalities in the case of environmental economics. At the policy level, the interaction of trade and environmental policies is increasingly recognised by both analysts and policy-makers as central to the successful operation of both.Two key areas of policy concern have motivated recent studies of the tradeenvironment nexus. One is the fear that trade liberalisation will increase pollution emissions, which raises the issue of whether environmental policy should be tightened to compensate for changes in trade policy. A second major focus of linkages between the two areas is the debate over environmental regulation and international competitiveness. Ongoing debates about increased environmental regulation in the EU have renewed fears that such measures could reduce on competitiveness, leading to both deindustrialisation and "carbon leakage" as polluting industries relocate to other countries. The net effect would be to shift the costs of environmental degradation but also the benefits of industrial agglomeration towards foreign and away from domestic locations.To explore these issues, I consider three alternative approaches to modelling the interaction between trade and environmental policies. First, I consider the benchmark case of a competitive small open economy and review the familiar but important second-best considerations, which can make lax environmental policies desirable if trade policy is constrained, or tariffs welfare-improving when environmental policy is constrained to be suboptimal.Next, I consider models of technical choice by polluting oligopolists. Once again, it turns out that second-best considerations complicate the ranking of alternative interventions.