El Derecho Internacional como fuente del Derecho Constitucional

This article has the purpose to prove that the Customary InternationalLaw and the Conventional International Law are sources of Constitutional Law. First, it analyses the matter of the relations between International Law and National or Domestic law according withthe theories dualism and monist and international decisions. Then, itstudies the reception and the hierarchy of International Customary and Conventional Law to Domestic Law including Constitution. This matter has been studied according with several Constitutionsand the international doctrine. Then, it considers the constitutional regulations about international law in the Constitution of theRepublic of Colombia.The general conclusion is that International Law is incorporated indomestic law according with the Constitution of each country. Butevery state has the duty to carry out in good faith its obligationsarising from treaties and other sources of International Law, and itmay not invoke provisions in its Constitutions or its Laws as anexcuse for failure to perform this duty. Accordingly, state practiceand decided cases have established this provision, and the same ruleis established in articles 27 and 46 of the Vienna Convention on Lawof Treaties of 1969.