International law has always had a dual significance to the Philippine constitutional system. On the one hand, the frequent articulation of international law principles within modern Philippine constitutional norms, statutes, and administrative rules demonstrate an outward-looking normative ethos – one I have described in other scholarship to be consistent with the 1987 Philippine Constitution’s ‘universalist history’. On the other hand, the considerable volume of Philippine jurisprudence applying international law norms to date overwhelmingly illustrate how Philippine litigants have strategically deployed international law (most especially international human rights law) over the years, as an acceptable external legal basis to hold Philippine government leaders to account under the vastly expanded judicial review doctrine in the 1987 Philippine Constitution. This active individual and group resort to adjudication and legislation could explain why international law has flourished under the postcolonial and post-dictatorship 1987 Philippine Constitution. This comprehensive jurisprudential, statutory, and constitutional analysis aims to show how, and to what degree, Philippine legal culture and history reflect a continuing deep engagement with international law, in ways that are certainly unique to the Philippines’ evolving political ideologies, colonial and postcolonial history, treatment, and implementation of international treaties within the Philippine constitutional system. Most importantly, the absence of explicit methodology for the breadth of constitutional interpretation of the Incorporation Clause under the 1987 Philippine Constitution warrants normative rethinking, so as not to uniformly open the floodgates to hard international law sources (eg treaties, customs, general principles) as well as softer international instruments lacking the requisite State consent to the binding quality of such sources within the Philippine legal system. To this end, I make three proposals on how the Philippine Supreme Court could define an explicit methodology for use and interpretation of the Incorporation Clause, transparently refer to other foreign and international sources, and openly reassess its ideological bases for recognition of international law in the Philippine constitutional system, as part of the Court’s distinct judicial function.