“Executive functions” is an umbrella term for functions such as planning, working memory, inhibition, mental flexibility, as well as the initiation and monitoring of action. The impairment of executive functions in various clinical groups is a topic of much debate, as are recent attempts to formulate the corresponding intervention and rehabilitation regimes of these dysfunctions. This article reviewed current theories of executive functions and their associated assessment instruments. In addition, it identified issues that are imperative for more accurate, sensitive, and specific assessment of various components of this construct. It is concluded that more research is needed to fractionate the executive system by assessing a wide range of functions and to verify their neuroanatomical correlates. Recently developed measurement models and technology may also facilitate a more ecologically and ethologically valid assessment for the specific needs of different individuals.