The ability to challenge substantive theories on their home ground has sometimes led to the false impression that Constructivism is a substantive theory that it is. As such, it is much more and much less than meets they eye. It is much less because it is not properly a theory that can be viewed as a rival to already existing theories. It offers no predictions about enduring regularities or tendencies in world politics. Instead, it suggests how to investigate them. Consequently, it is much more than meets the eye because it offers alternative ways of thinking about a range of issues. Contructivists have offered alternative formulations of the basic concepts and theories that matter to Realists, including the nature of power, alliance formation, war termination, and military intervention. They have offered important insights into the liberal peace. They have offered critical amendments to neo-liberal Institutionalism as they have investigated alternative causes and consequences of international institutions and organizations. Although Constructivism does not have same analytical rigour that is one of rational choice’s strengths, its thematic reach is comparable.