ABSTRACT Participation is the best social way for solving environmental problems. In this researching work, a methodology for public participation is trying to be developed by analyzing different projects and watching how different claimants have been participated and the types of the more frequent allegations, because public participation is going to be a key tool in the processes of Environmental Impact Assessment. When we talk about participation, we aren’t talking about popular queries or isolated consensus. We are talking about multidimensional processes in which education, legal aspects, organization, pure participation techniques and other social action areas are working in parallel and go on, feed-backing and reinforcing one each other. In the present Thesis is included all the legislation about public participation in chapters 2 and 3 and the different public participation techniques in chapter 4 and some remarks about environmental education; all these topics are very important for a good public participation. Following types of projects have been selected, because of the greater quantity of allegations and valid data found for this Thesis: roads and highways, airports, thermal power stations, electric lines, railway webs, pipelines, hydrological projects. The methodology for analyzing the projects includes searching and obtaining of the already developed projects or currently in process of development, as well as presented allegations and queries. In the second place, participants are analyzed in a methodical way in four groups. Types of allegations have been identified and classified. Tables and charts, that match participation of each type of claimer to their allegations for each project have been built, with the aim of obtaining a more summarized information and better organized, for extracting better conclusions of each project regarding environmental, legal and structural aspects. The established scale is flexible and was carried out by seeking advice from experts. Depending on number of claimers versus allegations, projects may be improvable, unacceptable or correct2. Environmental improvements by means public participation can be found in final conclusions for each project. Finally, a methodological proposal is developed and in the last chapter final conclusions and future forecast are commented. By means of case analysis, it has been verified that when associations are active, representative and especially large and well coordinated, it allows a more satisfactory participation and the undertaking of important projects or even the planning of the management of the field that affects them. Participation may and must undertake all types of problems, from the most local to the most global; the complexity and scope of the challenge shouldn’t be limiting since we approach to the solutions of big problems if we take advantage of the consensus and of the richness of contributions given by participation. The advantage of participation is that this process is more transparent, the application of solutions better fitted to the necessity, in agreement with the resources and better assumed by the implicated parties. The solution itself will be more solid and transparent than if it were thought by an exclusive team of technicians or controlled by rules that have a difficult explanation.