Within the last decades, corporate information technology (IT) environments have approached considerable degrees of complexity. As a consequence, IT has become increasingly difficult to manage resulting in high costs and poor flexibility. Today, it is generally acknowledged that the sustainability of corporate IT environments can only be ensured through a continuous and long-term management on the level of the Enterprise (IT) Architecture (EA). To address this, many firms have implemented a dedicated Enterprise (IT) Architecture Management (EAM) function. However, little is known yet on the effectiveness of such functions and the factors influencing EAM success. Within this research, we thus seek to answer two main questions: (1) do firms adopting EAM perform better with regard to high-level information management objectives like IT flexibility and IT efficiency, and if so, (2) what are the critical success factors in attaining these goals? To answer these questions, a field survey was conducted within the international financial services industry. The results provide evidence that the implementation of an EAM function is in fact supportive in the creation and sustainment of IT efficiency and IT flexibility. Several factors are shown to be of critical importance for achieving these goals with architectural governance being the most important one.