This article shortly reviews the different stages of management to emphasize the close relationship that, in every historical period, the social conditions of the time and the approach to organization management have had. In the last few years, the organizational change has become the key concept, and we have seen a wide range of methods and techniques for management and leadership emerging, but a new general theory of organizations has not been defined. This has resulted in increasing insecurity and uncertainty among managers that see how the methods that they use cannot cope with the new challenges. This article seeks to find, in the emerging paradigm of complexity, the basis to integrate and give coherence to the different management and leadership methods, and then extrapolate the characteristics of complex systems to the basic roles of leadership. Moreover, it emphasizes the need to change our mental models in order to integrate the consequences of managing complexity.