Traced back to the writings of Grotius and Vattel, the doctrine of lex specialis has been the focal point in the ongoing debate on the fragmentation of international law. While international economic law has been envisaged as a specialized field in the adjudicative ambit of which normative conflicts often arise, it appears that only sporadically lex specialis has been specifically scrutinized in the context of international economic adjudication in general, and the World Trade Organization (WTO) adjudication and investment arbitration in particular. For, despite the rather often invocation of lex specialis in international trade and investment disputes, a considerable degree of generality and vagueness still appears to surround the more detailed aspects of its normative operation. In fact, the continuously growing body of panel and Appellate Body jurisprudence and the numerous investor-state arbitrations indeed feature repeated instances of recourse to the concept, perhaps now more (in numerical terms) than in any other field of public international law. At the same time, and now in qualitative terms, a closer look at these two seminal adjudicative aspects of international economic law provides the opportunity to draw insights that have also merit in the greater field of international dispute resolution. Ergo, as a first step dual typology of lex specialis is examined, so as to draw the line between the lex specialis derogat generali principle and the lex specialis/generalis qualification. Then, as a matter of normative methodology, it is demonstrated, inter alia, that the proper operation of lex specialis derogat generali denotes the juxtaposition of two specific norms. Additionally, it is argued that lex specialis is equally characterized by the normative equivalence of the juxtaposed norms, translated in a requirement for a rather high degree of rationae materiae sameness in terms of both their normative content and function. With these propositions in mind, the argument finally unfolds further so as to offer insights on the obscure issue of normative priority between lex specialis derogat generali and lex posterior derogat priori (later treaties supersedes earlier treaties) as expressed in the Vienna Convention, to then conclude with certain more generic remarks linking the analysis on lex specialis with the rationae materiae aspect of international legal disputes now, so that, overall, the conclusions reached can potentially also find general application outside the four corners of international economic law adjudication. Presented at the SIEL 2010 Conference in Barcelona.