The study was developed in a sample of 250 individuals (n=250) over 18 years of age who were eligible voters in Portugal, and aimed primarily to evaluate citizens' opinions of the public participation context of environmental and spatial planning, considering two points, (1) who should be involved in the decision-making process, and (2) during which stage of the decision-making process of public policies citizens should be involved and should participate. The majority of the sample (64.8%) reported that do not participate in environmental and spatial planning policies. Some 94.8% of the sample considered that all the stakeholders (governments, private organizations, and common citizens) should be involved in public policies, and the majority of respondents (82.4%) considered that the population should participate and be involved "from the very beginning of the project development"-that is, at the embryonic idea time. The type of value that every citizen attaches to politicians' actions and/or decisions and the level of public participation in environmental and territory planning policies, resented a statistically significant relationship (p = 0.014). Citizens can and should, be involved in decision-making processes in the early stages and should have the opportunity to truly influence the decisions handed down. It is the planner's obligation to valorize information and build partnerships, to document participation activities and their results, and to explain at the end how the participation influenced the final decisions made.