Over the duration of a project, a number of roles can and will try to influence the course the project will take. While some of these influencers are quite readily ap-parent because they are formal decision makers involved in some form in the pro-ject organization, others are not easily identified. In big projects there can be a big number of informal influencers who try to alter the course of a project with their own agenda in mind. That is not always beneficial for the project, and the project manager can have a hard time identifying and managing these informal influences. The purpose of this paper is to show if there are ways of recognizing these influ-encers, and if there are methods to successfully manage them in a way that is beneficial for the project. From the theoretical background of decision making models, project phases, project management basics and theories of power in or-ganizations, hypotheses are formed, which are then challenged against the input from the experts interviewed in the practical part. The empirical data was gathered via interviews with project managers from different national and international com-panies. The results show that while influencing the formal, visible decision makers in a project is commonplace, it is very difficult for project managers to even identify the informal decision makers who work behind the scenes. Most of the time only the results of the interventions can be recognized, but to be able to identify these informal decision makers soon enough takes a lot of experience and effort.