In his EJIL Foreword, Jan Klabbers argues that the contemporary application of functionalism, understood as organizations being assigned functions, in order both to realize the common good and to deepen inter-state cooperation, is something of a theoretical straitjacket. However, can functionalism really be described as a ‘one-size-fits-all' concept? It is the contention of this Comment that there are, in fact, different manifestations of the concept, including neo-functionalism and formal or informal functionalism. New realities in this field also reflect an evolved conception of functionalism, such as the increasing diversity of actors affected by, and influencing, international organizations, as well as the fact that institutions have become authorities in their own right. As a consequence, we may also observe the emergence of principles, often referred to as global administrative law principles, aimed at dealing with these new realities. The article recognizes that a functional orientation in designing the mandates of international organizations has contributed to overlaps and inefficiency. However, it argues that efforts have been made in pursuance of greater efficiency.