International Legal Research in a Nutshell by What is Foreign Law?
Foreign Law refers to the law of another country or other countries (a.k.a "sovereign nations.") It may take the form of common law, civil law, customary law, religious law or a hybrid structure. It does not have effect outside of national boundaries. Primary sources include:
Some countries provide web based access to their laws, with translations. France is a good example.
German Employment Law: 618 Questions Frequently Asked by Foreigners by Comparative Law is the "study of the similarities and differences between the laws of two or more countries, or between two or more legal systems." Marci B. Hoffman & Robert C. Berring, Jr, International Legal Research in a Nutshell (2nd ed. 2017). It is not considered a body of law, by itself, but rather an approach to legal inquiry.
What is International Law?
International law. (18c) The legal system governing the relationships between nations; more modernly, the law of international relations, embracing not only nations but also such participants as international organizations and individuals (such as those who invoke their human rights or commit war crimes). Also termed public international law; law of nations, . . . law between states. INTERNATIONAL LAW, Black's Law Dictionary (Bryan A. Garner, Editor in Chief, 9th ed. 2009), international law.
Public International Law, governing relationships between: national governments, intergovernmental organizations, non-government organizations (NGOS) and individuals. Think of this as the law regulating these entities across national boundaries. Primary Sources of Law include: Treaties, Conventions, Decisions of the International Court of Justice (ICJ), customary international law, generally recognized principles of law and scholarly commentary. Relevant Topics:
Customary International Law. International law that derives from the practice of states and is accepted by them as legally binding. This is one of the principal sources or building blocks of the international legal system. One might think of it as a sort of common law springing from the consistent interaction of many nations over time. Principal features include:
Restatement (Third) of Foreign Relations, "customary international law results from a general and consistent practice of states followed by them from a sense of legal obligation." Primary Sources include:
See also Marci B. Hoffman & Robert C. Berring, Jr. , International Legal Research in a Nutshell (2nd ed. 2017).
Private International Law, a.k.a. International Conflict of Laws. The focus here is on the choice of law to apply when there are conflicts in the domestic law of different nations related to private transactions between those nations. Primary Sources of Law: national law. Common areas where this arises include:
Marci Hoffman and Katherine Topolos, International Legal Research Tutorial: Private International Law (last visited Dec. 20, 2019).
What is Transnational Law?
1. The amalgam of common principles of domestic and international law dealing especially with problems arising from agreements made between sovereign states and foreign private parties. 2. The problems to which such principles apply. Cf. international law.
TRANSNATIONAL LAW, Black's Law Dictionary (9th ed. 2009), transnational law
Normally, in international law, states are like billiard balls--they may knock each other around, but there is no inner penetration to provinces, municipalities, or individuals. In transnational law, this is not true; not only are nation states involved, but also sub-sovereign entities and individuals. This often occurs when there are environmental and shared natural resource issues.
The CIA World Fact Book summarizes transnational issues for each country. For instance, water sharing with the United States is listed as a disputed issue under Mexico's "Transnational Issues."
Another example is the Columbia River Treaty Review involving not only the sovereign states of the United States and Canada, but British Columbia, Oregon, Washington, Idaho, Montana, and Wyoming and fifteen tribal nations of the United States and seventeen first nations in Canada. See Nigel Bankes and Babara Cosens, The Future of the Columbia River Treaty 26-29, 102 (October 2012). https://munkschool.utoronto.ca/wp-content/uploads/2012/07/Bankes_and_Cosens_POWI_2012.pdf
Image from Center for Environmental Law & Policy, https://www.celp.org/programs/crt/ (last visited December 19, 2019).
The three-year commitment is being described as ‘historic’
JOHN BOIVIN Jul. 29, 2019 2:00 p.m.
As noted by the story, "leaders from three Indigenous groups and the provincial and federal governments have signed an agreement to bring salmon back to the Upper Columbia River. Representatives from the Syilx Okanagan, Ktunaxa and Secwepemc peoples, British Columbia and Canadian governments signed a letter of agreement in Castlegar on Monday.
“Our fundamental goal is to bring the salmon back to their historic range, the headwaters of Columbia Lake,” said Kathryn Teneese, chair of the Ktunaxa Nation Council.'"
What is Supranational Law? Think European Union. 
Supranational law is a form of international law, based on the limitation of the rights of sovereign nations between one another. Nations explicitly submit their right to make judicial decisions to a set of common institutions. Saskia I Mehlhorn, Fulbright & Jaworski LLP, Foreign & International Law Research (handout) 2 (Spring 2011); SUPRANATIONAL, Black's Law Dictionary (9th ed. 2009), supranational.
An example of a supranational institution is the European Union (EU) because it has sovereignty, including judicial review, over the member nation states in certain instances. See e.g., Fact Sheets of the European Union - 2013, Supranational Decision-Making Procedures.
As the European Court of Justice observed:
"The objective of the EEC Treaty, which is to establish a Common Market, the functioning of which is of direct concern to interested parties in the Community, implies that this Treaty is more than an agreement, which merely creates mutual obligations between the contracting states. This view is confirmed by the preamble to the Treaty, which refers not only to governments but also to peoples. It is also confirmed more specifically by the establishment of institutions endowed with sovereign rights, the exercise of which affects Member States and their citizens…"
Van Gend en Loos (N.V. Algemene Transporten Expeditie Onderneming van Gend & Loos and Nederlandse administratie der belastingen (Netherlands Inland Revenue Administration), Case 26/62 [1963]: Eurofound, EU Law.
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