INTRODUCTION
Custom is one of the principal elements of public international law, as laid down in the Statute of the International Court of Justice.Footnote 1 The rules of customary international law develop over time from the behaviour of sovereign states in the field of international relations; this behaviour is known as ‘state practice’. Dixon illustrates the formation of customary international law with this example: ‘…if all maritime nations declare a territorial sea 12 miles seaward from the coastline, a customary law may develop to this effect.’Footnote 2
In order for customary international law (CIL) to emerge, state practice must have been general and consistent and must also have arisen from a sense of legal obligation.Footnote 3 The element of obligation is referred to as opinio juris, short for opinio juris sive necessitatis, meaning ‘opinion that an act is necessary by rule of law’;Footnote 4 it is also described as the ‘subjective’ or ‘psychological’ element of customary international law. There are many different arguments as to the relative importance of state practice and opinio juris and their contribution to the formation of CIL, but these debates are the concern of lawyers, not librarians.Footnote 5
Because custom is itself unwritten, in order to research customary international law it is necessary to examine the evidence of state practice. This information is found in a wide variety of sources, including diplomatic correspondence, policy statements, press releases, the opinions of government legal advisers, military law manuals, government decisions and practices, orders to military forces, comments on International Law Commission consultations, legislation, the judgments of international and national courts, treaties, United Nations resolutions on legal issues and the practice of intergovernmental organisations.Footnote 6
It should be mentioned at the outset that many researchers will not have time to carry out extensive investigations of state practice. They will instead consult secondary sources of information, such as decisions of the International Court of Justice and books on international law.Footnote 7 The main focus of this article, however, is on the less familiar topic of sources of information about state practice. The main emphasis will be on the types of material listed in The IALL Guidelines for Public International Law Research Instruction,Footnote 8 that is, on diplomatic documents, foreign policy material, legislation relating to international law and the documentation of intergovernmental organisations. Since clear evidence of opinio juris is difficult to find, this aspect of CIL research will not be covered.Footnote 9
GENERAL STATE PRACTICE SOURCES
The Yearbook of the International Law Commission is a particularly valuable source for CIL research, because it brings together information about the policy and practice of many different states, in the form of national responses to the Commission's consultations. These responses appear in volume II of each Yearbook. The series is available on the International Law Commission's websiteFootnote 10 and is also on the subscription database HeinOnline, in the UN collection.
Another title covering a range of states is International Legal Materials (ILM),Footnote 11 a bi-monthly publication which reproduces, summarises or lists noteworthy documents relating to international law. The types of material covered by ILM include national and international court decisions, national legislation regarding international law, government submissions in legal proceedings (mostly from the US Government), policy statements and documents issued by intergovernmental organisations. Online versions of ILM can be found on Lexis (US version), HeinOnline and other databases.
UK PRACTICE
British Year Book of International Law
The leading source of information about UK practice is the British Year Book of International Law (BYBIL), published by Oxford University Press. From 1978 onwards, each volume has a section called ‘United Kingdom Materials on International Law’ (UKMIL), which reproduces noteworthy statements to Parliament, ministerial letters, legislation, submissions to international conferences and other documents. To help the researcher, UKMIL is systematically arranged by topic: for example, ‘Boundaries and frontiers: delimitation’. Cases relating to international law are summarised in a separate section of the Year Book, ‘Decisions of British Courts … Involving Questions of Public or Private International Law.’ BYBIL is available online via the Oxford Academic platform.
One of the forerunners of UKMIL was British Practice in International Law,Footnote 12 compiled in the 1960s by Elihu Lauterpacht and Gillian White, covering the period 1962 to 1967. It reproduced statements to Parliament and other documents of interest, again arranged by area of international law. British Practice in International Law was preceded by an irregular feature in International & Comparative Law Quarterly (ICLQ), entitled ‘The Contemporary Practice of the United Kingdom in the Field of International Law – Survey and Comment’ (1956 to 1961). The commentary in ICLQ gives the context, noting, for example, that the Diplomatic Immunities Restrictions Act 1955 ‘forms part of the international pattern of legislation on diplomatic immunities from which it is possible to ascertain the practice of States.’Footnote 13
A British Digest of International Law
A British Digest of International Law, edited by Clive Parry, aimed to be a statement of British practice in international law from 1860 onwards. It was to be compiled from the vast Foreign Office archives, whose daunting appearance Parry recalled, ‘…row upon row, ranged, amongst other places, in immensely long Nissen huts, and seeming to stretch into a far distance…’.Footnote 14 Several volumes of the work were published by Stevens & Sons in the 1960s, covering the period 1860 to 1914, but it was never completed.
British and Foreign State Papers
An important title covering about 150 years of British practice (1812 to 1967/68), British and Foreign State Papers (BFSP) was produced by the Foreign Office until the 1970s. It contains official statements, speeches, letters, communiqués and other documents that may constitute evidence of state practice. BFSP is not arranged by topic, unlike UKMIL and related titles, but it has indexes and there is a searchable version on HeinOnline.
Compiled diplomatic documents
A title with more of a historical than legal slant, but still of relevance, is Documents on British Policy Overseas. Compiled by historians from the Foreign and Commonwealth Office, it provides a record of British foreign policy since the Second World War. It has two pre-war companion series, British Documents on the Origins of the War 1898-1914 and Documents on British Foreign Policy 1919-1939. All three titles are available online, via ProQuest.
Parliamentary proceedings, speeches, press releases, diplomatic material
Researchers may want to trawl through raw documentation on official websites or at The National Archives, instead of relying on edited compilations. For official statements on international law, they can search the online version of Parliamentary Debates (Hansard) on the UK Parliament website (1803 onwards)Footnote 15 and useful material may also be found in the database of speeches, press releases and policy statements on the Gov.uk site.Footnote 16 Documents published on the websites of government departments from the mid-1990s onwards may be gleaned from the UK Government Web Archive, or the Wayback Machine.Footnote 17 The National Archives holds printed official records, including Foreign Office (and Foreign and Commonwealth Office) documents such as papers relating to diplomatic conferences, letters, memoranda and reports.Footnote 18
FOREIGN STATE PRACTICE
Yearbooks and journals of international law
Yearbooks of international law are available for many jurisdictions and regions. Examples include the Australian Year Book of International Law, L'Annuaire français de droit international (French yearbook of international law) and the African Year Book of International Law. Like the British Year Book, these publications usually have a state practice section reproducing or summarising policy statements, diplomatic material and other documents.
In some countries, state practice is reported by a quarterly or monthly journal, for instance, the American Journal of International Law (AJIL), which has a section called ‘Contemporary Practice of The United States Relating to International Law’. The French quarterly Revue générale de droit international public reports diplomatic incidents, military action, summit meetings, treaty developments and court decisions concerning a range of states, not just France, under the heading ‘Chronique des faits’.
The HeinOnline service is a treasure trove for international law researchers. Its Foreign and International Law Resources Database includes about fifteen national yearbooks of international law, several regional series and a number of topical ones (such as Ocean Yearbook), while its Law Journal Library contains other relevant titles, notably the American Journal of International Law.
Some yearbooks and journals are freely available on the internet, for example the Asian Year Book of International Law (2010 onwards),Footnote 19 Australian Year Book of International Law (1965-2009),Footnote 20 Annuaire Français (1955 onwards, with a three-year embargo)Footnote 21 and Heidelberg Journal of International Law (whole series, with a one-year embargo)Footnote 22. However, the same titles are often on HeinOnline or another subscription database, where there are usually superior search facilities.
WorldCat, the global library catalogue, is a useful tool for finding out what yearbooks and journals of international law exist.Footnote 23 Many are published in English, but to find series in other languages, search terms such as ‘anuario’ and ‘annuaire’ (Spanish/French for ‘yearbook’) can be used. Yearbooks and journals are also listed in bibliographies, such as Gaebler and Shea's Sources of State Practice in International Law and Beyerley's Public International Law: a Guide to Information Sources.Footnote 24
Foreign ministry bulletins and websites
Many foreign ministries publish policy statements and other relevant documents in an official bulletin or gazette. In the United States from 1939 to 1989, the Department of State Bulletin published speeches, statements, testimony before Congressional committees and US treaty actions. The Bulletin was continued by the Department of State Dispatch, 1990 to 1999; since this date the State Department website has been used to publish policy statements and other material. Both the Bulletin and the Dispatch are on HeinOnline. Foreign ministry bulletins from other jurisdictions are detailed in Gaebler and Shea's bibliographyFootnote 25 and a global directory of links to foreign ministry websites is provided on the website of the US Institute of Peace.Footnote 26 For older documents that were published on the internet, archived official sites may be available via links from the current foreign ministry's website, or via the Wayback Machine.Footnote 27
Compiled diplomatic documents
Some foreign states, like the UK, publish official collections of their diplomatic documents. The website of the International Committee of Editors of Diplomatic Documents provides a descriptive list of these publications, covering about twenty different countries;Footnote 28 details are also given in Gaebler and Shea.Footnote 29 Some collections of diplomatic material are freely available on the internet, for example, Documents on Australian Foreign Policy is on the website of the Australian Department of Foreign Affairs and Trade,Footnote 30 Foreign Relations of the United States is on the State Department websiteFootnote 31 (as well as on HeinOnline), and the German title Akten zur Auswärtigen Politik der Bundesrepublik Deutschland is on the website of the Institut für Zeitgeschichte.Footnote 32
Parliamentary proceedings
The websites of national legislatures often publish their proceedings (equivalent to Hansard in the UK). Links to parliament websites around the world can be found on the Inter-Parliamentary Union's Parline platform.Footnote 33 Printed parliamentary proceedings can be located using the Library Hub Discover or WorldCat union catalogues;Footnote 34 if you do not know the title, use an author search along the lines of nigeria parliament senate. (See Parline, or the Statesman's Yearbook, for the names of foreign legislatures.)Footnote 35 Alternatively, details of many series of parliamentary proceedings are given in the British Library’s guides to foreign official publications.Footnote 36
Digests
A few states have published systematic digests of their practice in international law, compiled by expert lawyers and arranged by international law topic. These titles often include unpublished documents from government archives. Most of them are not very up-to-date in their coverage, however, because producing an international law digest is a very onerous task.
Several successive digests have been compiled by the US State Department, the current title being Digest of United States Practice in International Law (1973 onwards).Footnote 37 For Brazil there is a digest called Repertório da prática brasileira do direito internacional público, covering 1889 to 1981,Footnote 38 and France has the Repertoire de la pratique française en matière de droit international public, going from 1789 to the early 1960s.Footnote 39 Other digests are listed in bibliographies and research guides.Footnote 40
Concise digests are also available, such as International Law in the Netherlands (three volumes) and Dugard's international law: a South African perspective (one substantial volume).Footnote 41 These shorter works do not reproduce documents, but give an overview of a particular state's practice, topic by topic.
Legislation concerning a state's international obligations
Legislation relating to international law is another type of material that may provide evidence of state practice. Many yearbooks and digests of international law cover legislation concerning international obligations, but researchers might also like to use a source that covers a wide range of jurisdictions. The UN's Legislative Series does this: founded with CIL research in mind, it reproduces or summarises national legislation concerning international law from around the world, with commentary. Each volume focuses on a particular topic, such nationality, diplomatic and consular law, or state succession. The Legislative Series is in the UN Law Collection on HeinOnline and recent volumes are on the UN website.Footnote 42 Legislation from many different jurisdictions is also found in specialist encyclopedias, such as the looseleaf work, International Immigration and Nationality Law.Footnote 43 Another wide-ranging source (for those who read French) is the Annuaire de législation française et étrangère, which publishes legislation from France and francophone Africa.Footnote 44
For detailed guidance on tracking down foreign legislation, the subscription database, Foreign Law Guide: current sources of codes and basic legislation in jurisdictions of the world is an excellent global resource.Footnote 45 It has citations to legislation from almost every jurisdiction, arranged by topic, with references to translations of foreign laws (if any) and links to collections of legislation on the internet. If Foreign Law Guide is not available, the free foreign law research guides on New York University's Globalex website may be used to look up the titles of national legislative publications and find links to legislation websites.Footnote 46
PRACTICE OF INTERGOVERNMENTAL ORGANISATIONS
CIL research is not only about the practice of states: the activities of intergovernmental organisations (IGOs) such as the United Nations and European Union may also contribute to the formation of customary international law.Footnote 47
United Nations sources
The practice of the General Assembly and Security Council, as well that of other UN organs, is recorded in the Repertory of Practice of United Nations Organs and the United Nations Juridical Yearbook; both are available on the internetFootnote 48 and in the UN Law Collection on HeinOnline. The Repertory summarises decisions by the principal UN organs under each article of the UN Charter, while the Juridical Yearbook (Part II) covers the legal activities of the UN. Researchers who do not have access to HeinOnline can use the UN's Legal Publications Global Search,Footnote 49 which covers both titles.
Other UN sources include Repertoire of the Practice of the Security Council and Resolutions and Decisions Adopted by the General Assembly, both of which are on HeinOnline. The Security Council Repertoire is also on the UN website, and resolutions of the General Assembly and Security Council are available in the UN Official Documents System (ODS).Footnote 50
The practice of the UN human rights bodies is recorded in their recommendations, concluding observations, reports and other documents. Most of this material is in the Official Documents System, but there are also specialist UN human rights databases, which can be searched by country (unlike the ODS). The UN Charter Body Database contains resolutions, reports and other material produced by the Human Rights Council (HRC), the Commission on Human Rights (its predecessor) and their subsidiary bodies; the Treaty Bodies database contains recommendations, concluding observations and other documents produced by the numerous UN human rights committees; the Jurisprudence database contains recommendations and findings by human rights committees in cases regarding complaints by individuals; and the Universal Human Rights Index contains recommendations, reports and concluding observations issued by both Charter-based and treaty-based human rights bodies.Footnote 51
Further information about United Nations material may be found in the online guides by the UN's own Dag Hammarskjöld Library.Footnote 52 A detailed UN research guide is also available on Columbia University's website.Footnote 53
Other intergovernmental organisations (IGOs)
Documentation of IGOs other than the UN is available on their websites and older material is held at the British Library, LSE Library and elsewhere.Footnote 54 The internet offers many research guides covering the official publications of IGOS: a good starting point is ‘UN & Intergovernmental Organizations,’ provided by University of Toronto Libraries.Footnote 55 Globalex has a collection of guides covering a large number of IGOs, and research guides for the EU and Council of Europe are available on IALS Library's website.Footnote 56
CONCLUSION
There are so many sources that could be used to research state and IGO practice in international law that it is only possible to highlight leading titles and a handful of other illustrative examples; for foreign state practice, in particular, an exhaustive survey would not be feasible. However, additional information is given in the bibliographies, internet gateways and library catalogues referred to in each section above.
As mentioned at the beginning, books, encyclopedias, International Court of Justice rulings and other secondary sources often have to be used as a substitute for original research, because it is so time-consuming to gather and analyse the evidence of state practice. There is some good news for specialists in international humanitarian law, however: the International Committee of the Red Cross (ICRC) has published a detailed, systematic study of customary rules, entitled Customary International Humanitarian Law.Footnote 57 This appears to be the Holy Grail of CIL research, as far as humanitarian law is concerned. However, although the online version of the ICRC study won an award from the American Society of International Law in 2015,Footnote 58 and the rules that it sets out have been cited in court,Footnote 59 it has been criticised by the US government.Footnote 60 This lack of consensus is far from unusual in the field of customary international law, which is what makes it such an interesting, if bewildering, field.
