As stated above, a regime is defined by Stephen D. Krasner as a set of explicit or implicit "principles, norms, rules, and decision making procedures around which actor expectations converge in a given issue-area". This definition is intentionally broad, and covers human interaction ranging from formal organizations (i.e., OPEC) to informal groups (i.e., major banks during the debt crisis). Note that a regime need not be composed of states.[2]
Within IPE there are three main approaches to regime theory: the dominant, liberal-derived interest-based approach, the realist critique of interest-based approaches, and finally knowledge-based approaches that come from the cognitivist school of thought.[3] The first two are rationalist approaches while the third is sociological.
Within regime theory, because regime theory is by definition a theory that explains international cooperation (i.e., it's a traditionally liberal concept) liberal approaches prevail within the literature