1. Introduction while recognizing the importance of the various reports that enable documenting the environmental impact assessment, such as preliminary reports and environmental impact statements, this chapter only will analyse given environmental impact studies the central role in the process. They allow you to document all the analysis of the environmental impacts of a particular action such as different alternatives for its implementation, mitigation and/or compensation measures, and follow-up plans, monitoring and control. In addition, they are the source of primary information for those institutions that must speak out about a proposed action. On the other hand, an environmental impact study is a set of studies tecnicocientificos, systematic, interrelated, whose objective is the identification, prediction and assessment of the positive or negative effects that can produce one or a set of actions of anthropic origin on environment physical, biological, or human. Information provided by the study should allow reaching conclusions about the effects that can produce the installation and development of an action or project on their environment, establish measures to be implemented to mitigate and monitor impacts, to propose the necessary contingency plans. 2. Features of the studies of environmental impact environmental impact studies have certain characteristics that they own, without which could not comply with the objectives and benefits that have been identified as a useful tool in environmental protection. Some of them include aspects such as: predictive studies supported by scientific information; scanning multi and interdisciplinary, where different specialists must interact to achieve a comprehensive view of the variables in study; analysis of the different aspects involved through a peer resolution data to establish relations between them and so that they can be interpreted as a whole; environmental analysis the actions in a very diverse methodological framework, so the choice of the most appropriate methods requires generally a knowledge initial activity or project to run and the General characteristics of the territory or the place where the activity will be deployed.