Agency theory provides a framework which enables organizations to analyze, explain and understand the existing relationships between two key players; the agent and the principal, who -according to this approach- are under asymetric information and divergent interests. As usually happens in all disciplines, in recent years, a series of advances has been developed, that not only deliver new elements to consider, but also can extend the scope of the theory to better understand the reality of the companies. This paper's primarily aim, is to analyze the advancements occurred in the field of AT with an exposed literature review. Firstly to clarify AT elements, as well as how it can be used to evaluate behavior. Secondly, new developments and applications of the theory are shown to finally display a practical assessment of the work performed.