When the presidential candidate Clinton announced that he would not support NAFTA without environmental and labor side agreements, and during the period before NAFTA's ratification by the American Congress, Mexicans lived in most tense suspense. Even though, the idea of an environmental side agreement seemed to please most environmentalists in Mexico who hoped that this would lead to creating a major environmental conscience in the Mexican government. The purpose of this thesis is to elaborate a critical analysis of the North American Free Trade Agreement, its related documents and their effects concerning the environment, specifically its legal protection. We will start with a brief resume of the relations of trade and environment, then continuing with an overview of the document's history and provisions, analyzing the document's effects in Mexico, the nation that should be mainly concerned with the environmental effects of NAFTA, and, finally, conducting a brief comparison with what is happening with the European Union, concerning trade-environmental issues, before we reach the proper conclusions.