Complexity is an inherent property of all systems and a result of interconnections. In projects various systems come together to deliver the required outcome(s). The most common type of project complexity mentioned / considered in practice is the technical complexity and this has always been considered a main factor which affects project performance. Despite that, projects are delivered by people who interface ontinuously and therefore are effected by complexity, and in particular that caused by socio-organo interfaces and the boundaries between the various teams and parties. This has not been investigated. ocio-organo complexity leads to reduction in performance if interconnections are not managed. Research has been carried out to understand the effects of complexity through project management processes on project schedule and performance, aiming towards the development of a tool and identification of actions that will enable the management of these effects. The author presents results of five case studies, which demonstrate that socio-organo complexity affects performance and these results have similarities with the behaviour of underdamped control systems. The results have significant implications on the way socioorganisational complexity can be managed, how processes are implemented, but also enable parallels to be drawn between the fields of project management and control systems. Considering control systems theory proposals are made in this paper for actions to be taken which will contribute towards the management of the effects of socio-organo complexity on projects.