Public international law, as traditionally defined, is the law governing relations between nation states.
Foreign law is simply the national law (also known as domestic or municipal law) of another country.
Private international law is a confusing term in that it refers to the national laws governing the interactions of private entities and individuals, who happen to be from different nations. The question that arises in such instances is "which country's law applies?". Private international law is, therefore, sometimes referred to as conflicts of laws. A number of private international law topics are covered by treaty (i.e. family law, estates and trusts, litigation). Since treaties are characteristic of the public international law system, the application of treaties to private international law issues can be confusing as well.
The sources of public international law are enumerated under Article 38 of the Statute of the International Court of Justice, which is appended to the Charter of the United Nations. Those sources are, as follows: treaties, custom, general principles and case law and scholarly commentary as a subsidiary means for determining the rules of law. Treaties, custom and general principles are primary sources of law in the public international legal system. Court decisions and scholarly writings are secondary sources. Treaties are written agreements between nations. Customary law is state practice which is done out of a sense of obligation. General principles are those general legal principles which courts all over the world have recognized. Note that the documentation of inter-governmental organizations (IGOs) like the United Nations or so called "soft law" is not listed as a source of law under the ICJ Statute, perhaps because the Statute was drafted before the proliferation of IGOs.
Treaties are written instruments which can be found in several sources, both official and unofficial. In contrast, custom and general priniciples are not written down. Evidence of custom and general principles must be derived from other sources, such as treaties, UN documentation and court decisions.
The purpose of this guide is to introduce researchers to basic treaty and other sources for researching public and private international law. In addition, this guide will cover foreign law research and specific topics in international law, including international human rights law, intellectual property, international trade and international environmental law.
This response is based on “Citing UN Materials: Issues and Strategies,” DttP: Documents to the People 41:3 (Fall 2013).
For citation within United Nations documents, please use the United Nations Editorial Manual as the style guide for citation.
For external citation of United Nations materials, authors should comply with the system being used by their publisher or recommended within their institution. Authors will note that many standard systems of citation do not provide much information on citation of United Nations materials. The Bluebook: A Uniform System of Citation, which is used in the legal field, does have detailed guidance on citation of United Nations materials. The Chicago Manual of Style and APA Style point to The Bluebook for citation of United Nations materials.
The Dag Hammarskjöld Library does not recommend a specific citation system. Generally, authors may wish to include (a) the identity of the creator, (b) title, (c) publication date, (d) any unique identifiers, including functional URLs, and (e) any relevant page or paragraph numbers. Official United Nations documents carry unique identifiers called document symbols that are described in the UN Documentation Research Guide on symbols.
Authors should exercise caution when including URLs for official United Nations documents. URLs generated by the Official Document System (ODS) do not work. Authors can generate working URLs by adding the document symbol to http://undocs.org, e.g., http://undocs.org/A/RES/67/97.
Some possible citation examples for external authors, inspired in part by the United Nations Editorial Manual and The Bluebook, are as follows:
General Assembly resolution 67/97, The rule of law at the national and international levels, A/RES/67/97 (14 December 2012), available from undocs.org/A/RES/67/97.
United Nations, General Assembly, Situation of human rights in the Democratic People’s Republic of Korea: report of the Secretary-General, A/63/332 (26 August 2008), available from undocs.org/A/63/332.
Convention on the Recognition and Enforcement of Foreign Arbitral Awards, New York, 10 June 1958, United Nations Treaty Series, vol. 330, No. 4739, p. 3, available from treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXII-1&chapter=22&lang=en
United Nations Commission on International Trade Law, UNCITRAL Model Law on International Commercial Arbitration 1985: with amendments as adopted in 2006 (Vienna: United Nations, 2008), available from www.uncitral.org/uncitral/en/uncitral_texts/arbitration/1985Model_arbitration.html.
United Nations, Department of Public Information, Demanding that Lord’s Resistance Army End All Attacks, Security Council Calls for Full Implementation of Regional Strategy in Central Africa. SC/11018, 29 May 2013, www.un.org/News/Press/docs/2013/sc11018.doc.htm.
“Crime as an Impediment to Security and Development in Africa: Best Practices and Institutional Opportunities” (Side event summary report, United Nations, High Level Meeting On Africa’s Development Needs: State of Implementation of Various Commitments, Challenges and the Way Forward, New York, 22 September 2008), www.un.org/ga/president/62/ThematicDebates/adn/crimeimpedimentsd.pdf.
 The Bluebook: A Uniform System of Citation, 19th ed.(Cambridge: Harvard Law Review Association, 2010), 21.7.
 Chicago Manual of Style, 16th ed., 14.316 – 14.317; Melissa Shella, “Citing the Charter of the United Nations,” APA Style Blog, May 23, 2013, http://blog.apastyle.org/apastyle/2013/05/citing-the-charter-of-the-united-nations.html.