Guide last updated by Hester Swift, September 2024
This guide was created by Hester Swift, Foreign & International Law Librarian at the IALS Library.
Email hester.swift@sas.ac.uk
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We also recommend the following online research guides for international law.
Public international law governs the conduct of states and international organisations and the relations between them. Areas of public international law include air law, diplomatic law and the law of armed conflict.
The Statute of the International Court of Justice, article 38(1), is often used to define the sources of public international law. It lists the following sources: treaties; international custom (hence 'customary international law'); generally recognised principles of law; judicial decisions; and the teachings of publicists (leading scholars in the field of public international law). Judicial decisions and the teachings of publicists are classed as secondary sources (art. 31(1) (d)).
IALS Library has a large public international law collection, comprising treaty series; international law reports; hundreds of yearbooks and journals; and thousands of monographs. A large area of the third floor reading room is devoted to international law, while additional holdings are kept in the basement Reserve and Offsite Store. IALS also subscribes to many online databases with substantial international law content.
A treaty is a written agreement between two or more states, governed by international law (Vienna Convention on the Law of Treaties, 1969, art.2(1)(a)). It does not necessarily have the word 'treaty' in its title: it could call itself a 'convention', 'agreement', or something else.
Treaty glossary
Some common terms are listed below; for others, see the UN's Treaty Handbook and glossary.
General treaty sources
The entire UNTS is available free on the UN Treaty Collection website, with details of signatures, ratifications and so on; it is also in HeinOnline's UN Law Collection. IALS has the bound set up to vol. 2174 (2002), including cumulative indexes.
Regional treaty sources
The websites of regional bodies such as the African Union, the Council of Europe and the Organization of American States (OAS) provide treaty texts and status information: when the treaty entered into force, who has signed, ratified and so on.
The two-volume African Treaty Collection - treaties adopted by the Organization of African Unity / African Union between 1963 and 2022 - is available to download from the website of the African Institute of International Law.
Printed treaty series are published by some regional organisations. Examples include the Council of Europe Treaty Series (CETS) (formerly European Treaty Series, or ETS) and the OAS Treaty Series / Serie sobre tratados. IALS holds the entire ETS/CETS, 1949 onwards (FOL GO1.A.20.E.1) and the OAS series from 1970-1985 (RES SG40.J.19).
The FCDO Treaties page has links to recent treaties.
Treaties involving the UK are published as command papers (a type of official publication, now published online). There are four different series of treaty command papers: the Country series publishes newly-signed bilateral treaties; the Miscellaneous series publishes new multilaterals; the European Communities / Union series published EC/EU treaties, until Brexit; the Treaty Series (cited as 'UKTS'), which publishes treaties that have come into force for the UK. IALS Library does not have the Country series; it has:
- UKTS 1892 to 2020 (RES SG40.J.5 and FOL SG40.J.5 );
- EC/EU series 1974 – 2017 (FOL SG40.J.16);
- selected items from the Misc. series, catalogued individually.
Other national treaty sources
Publication of treaties in official gazettes is typical of civil law jurisdictions, but is also seen in some common law jurisdictions, for example, Singapore. IALS does not hold gazettes, but the British Library has a large collection.
Treaties by subject
Selected subject-based collections are listed below:
Historical treaty collections
Clive Parry's Consolidated treaty series (CTS / Consol TS) is an important collection of treaties concluded between 1648 and 1920. IALS Library has the whole series (more than 230 volumes).
HeinOnline's World Treaty Library is a vast collection of treaties from 1648 onwards. For historical treaties, it has very similar coverage to the Consolidated Treaty Series; it also includes thousands of more recent treaties, up to the present day.
Other historical collections available from IALS Library include: -
See also: the Avalon Project: documents in law, history and diplomacy (Yale University), which includes key treaties from the ninth century onwards.
IALS Library has a collection of treaty indexes (classmark BS40); various online indexes are also available.
Global indexes
FLARE Index to Treaties: free web resource provided by IALS Library, covering about 2,000 multilaterals (seventeenth century onwards) and some bilaterals (1353 to 1815). Gives citations, place and date of signature, et cetera, and links to the full text where available.
HeinOnline's Treaty Index (part of the World Treaties Library): covers the period from 1648 onwards; available via IALS Law Databases page.
Bowman, M. and Harris, D., Multilateral Treaties: Index and Current Status (Butterworths 1984) and 11th Cumulative Supplement (1995). Arranged chronologically, with subject and keyword indexes; gives citations, location, parties, signatories and status. The online FLARE Index to Treaties (see above) is partly based on the contents of Bowman and Harris.
Rohn, P., World Treaty Index (2nd edn, ABC-Clio 1984): covers bilaterals and multilaterals, 1920-1984. Offers access by keyword, parties, date, or subject. Has been incorporated into HeinOnline's Treaty Index.
World Treaty Index: updated version of Rohn's index (see above), covering over 55,000 twentieth century treaties, bilateral and multilateral.
Parry, C. and Hopkins, C., An index of British Treaties: 1101-1988, covers bilaterals and multilaterals.
UK Treaties Online, the official treaty database, indexes bilaterals and multilaterals from around 1835 onwards.
Kavass, United States Treaty Index (also known as Kavass's Current Treaty Index) covers treaties and agreements 1776 onwards. IALS has the hard copy; also in HeinOnline’s US Treaties and Agreements Library.
Treaties in Force (TIF): the current edition is on the State Department website; both current and previous editions are on Lexis, Westlaw International and Hein Online; the hard copy is held at IALS from 1964 to 2020 (print publication has now ceased).
Kavass’s Guide to the United States Treaties in Force: covers treaties and international agreements, 1776 onwards. IALS has the hard copy; also in HeinOnline’s US Treaties and Agreements Library.
Working documents produced during the drafting of treaties are known as 'travaux préparatoires'. They are not usually available outside institutional archives, but those relating to some of the more important treaties have been published, for example, Lee Swepston, The Foundations of Modern International Law on Indigenous and Tribal Peoples: the preparatory documents of the Indigenous and Tribal Peoples Convention, and its development through supervision (Brill, 2015-2018) (held at IALS).
Ryan Harrington's list of Collected Travaux Préparatoires, on Yale University's website, is a good place to start researching the drafting of a treaty. It gives details of available travaux préparatoires, print and online. Many of the print publications it mentions are held at IALS Library.
For further guidance, see:
Jonathan Pratter, 'À la Recherche des Travaux Préparatoires: An Approach to Researching the Drafting History of International Agreements', on New York University’s Globalex website.
Dag Hammarsköld Library (United Nations), 'What are travaux préparatoires and how can I find them?'
Customary international law develops when the general practice of states comes to be accepted as a legal obligation. For an introduction to the concept of state practice, see M. Wood, 'State Practice', in R. Wolfrum (ed.), The Max Planck Encyclopedia of Public International Law (print and online versions available at IALS - see Catalogue).
Researchers may find evidence of state practice in diplomatic correspondence, legislation, legal opinions, national and international court decisions, treaties, parliamentary debates and elsewhere.
Bibliographies of state practice material
A global bibliography of state practice material is annexed to the International Law Commission's memorandum, Identification of Customary International Law: Ways and Means for Making the Evidence of Customary International Law More Readily Available (A/CN.4/710/REV.1, 2019).
IALS Library holds printed bibliographies:-
Armin von Bogdandy and Anne Peters (ed.s), Public International Law: a Current Bibliography of Books and Articles (Springer, 1975 - 2015), section 1.2, 'Surveys of State Practice'. Also available on HeinOnline.
See also: Renu Urvashi Sagreiya, Researching Customary International Law, State Practice and the Pronouncements of States Regarding International Law (2024), on New York University's Globalex website.
State practice in yearbooks, journals and digests of international law
Yearbooks, journals and digests of international law provide information about state practice. They reproduce extracts from documents, summarise national court decisions in matters of international law and give details of treaty actions.
IALS holds a large collection of national yearbooks and journals of international law that cover state practice, and others are available online. Examples of titles available from IALS Library include:
The International Law Commission has estimated that periodicals publishing national state practice material are available for about thirty states (Identification of Customary International Law, A/CN.4/710/REV.1, 2019 [48]). A large majority of these titles are available at IALS Library in hard copy and or/online.
Regional yearbooks of international law also publish state practice material, for example:
The UN publishes several periodicals devoted to state practice and/or the practice of the UN itself:
The Max Planck Yearbook of United Nations Law is another periodical that summarises the practice of the UN and its agencies.
A few states have produced publications wholly devoted to state practice, for example:
There is also a compilation of state practice digests for Asian jurisdictions, The Encyclopedia of Public International Law in Asia (Brill, 2021).
State practice by subject
There are a few published surveys covering state practice in particular areas of law. They include the following:
State practice on official websites
Information about a state's current practice in the field of international relations may be found on the website of its foreign ministry: see WorldLII for links. Websites for state practice are also listed in Gaebler and Shea (ed.s), Sources of State Practice in International Law.
Decisions on international law matters are made not only by international courts and tribunals, but also by the courts of individual states (also known as 'municipal courts', in the international law context). Cases constitute a subsidiary source of international law (ICJ Statute, art.38(1)(d)).
General sources
The broadest collections of international law cases are found in the International Law Reports, Oxford Reports on International Law, International Legal Materials and WorldLII's International Courts & Tribunals Collection.
International Law Reports (ILR): the leading reporter of international law decisions in English, ILR publishes the decisions of international courts and tribunals as well as the decisions of municipal courts in matters of international law; it now includes more than 10,000 cases, from 1919 to the present day. ILR began in the 1920s under the title Annual Digest of Public International Law Cases (ADIL); formerly published by Longman, then Butterworths, it is now a Cambridge University Press title. IALS Library has the whole series, in print and online: see Catalogue.
Oxford Reports on International Law (ORIL): an Oxford University Press database of more than 5,500 international cases, from both international and municipal courts, mostly from the 1990s onwards; available via the IALS Law Databases page. Our ORIL subscription covers five modules: International Law in Domestic Courts (ILDC), International Courts of General Jurisdiction (International Court of Justice, etc.), International Criminal Law, International Human Rights Law, International Investment Claims.
WorldLII's International Courts and Tribunals Collection: this collection on the WorldLII website brings together cases from about thirty international courts and tribunals, plus UN committees. Generally speaking the content starts in the 1980s, 1990s, or later; however, for some courts it goes back much further. The content is not always current - the court's own website may be more up-to-date than WorldLII.
International Legal Materials (ILM): this series, produced by the American Society of International Law, publishes a selection of international law decisions with introductory notes. IALS holds the whole series (1962- ); it is also on Lexis+ (whole series), Westlaw International Materials (1980 onwards) and HeinOnline (up to pre-current volume); all these databases are available via the IALS Law Databases page.
National sources
IALS Library's holdings include the following national sources (print only):-
American International Law Cases: US court decisions on international law, 1783 to 2015.
British International Law Cases: British court decisions on international law, c.1600 to 1970, arranged by subject.
Commonwealth International Law Cases: a compilation of decisions from courts in Commonwealth countries, arranged by subject. Most of the cases date from the 19th century up to the 1970s.
National (municipal) court decisions on international law also appear in the International Law Reports and ORIL's International Law in Domestic Courts (both described above).
See also: yearbooks of international law, many of which have a section devoted to municipal court decisions on international law.
Decisions of individual courts
Each international court and tribunal provides its decisions on its own website and many also produce hard copy law reports. Selected courts are covered below: -
African Court on Human and Peoples' Rights: the court publishes its decisions in Report of Judgments, Orders and Advisory Opinions of the African Court on Human and Peoples’ Rights (Pretoria University Law Press, 2019 - ), which is held at IALS Library and freely available online from PULP.
Judgments, advisory opinions and other documents are available on the court's website. Selected cases are in the International Law Reports (ILR) and in the human rights module of Oxford Reports on International Law (ORIL); c ase commentaries are published in the African Human Rights Yearbook, International Legal Materials and other periodicals.
The Court of Justice of the European Union
For information about EU research, see IALS Library's European Union research guide.
European Court of Human Rights and European Commission of Human Rights
See IALS Library's Council of Europe research guide.
Inter-American Human Rights System (Organization of American States)
The websites of the Inter-American Court of Human Rights and the Inter-American Commission on Human Rights provide their decisions and associated information.
The official reports of the court are: Series A: Judgments and Opinions; Series B: Pleadings, Oral Arguments and Documents [relating to cases in Series A]; Series C: Decisions and Judgments; Series D: Pleadings, Oral Arguments and Documents [relating to cases in Series C]; Series E: Provisional Measures. These reports are freely available in the University of Minnesota Human Rights Library; they are not held at IALS.
At IALS Library, the largest source of cases from the Inter-American Court is probably Oxford Reports on International Human Rights Cases (see IALS Law Databases page); see also selected cases International Law Reports and International Legal Materials (ILM); ILM provides introductory notes to cases as well as the judgments. Another source held at IALS is Burgorgue-Larsen, The Inter-American Court of Human Rights: case law and commentary (OUP 2011; print and e-book).
The Inter-American Commission's decisions are published in the Annual Report of the Inter-American Commission on Human Rights, which is held at IALS from 1988/1989 to 2007 (incomplete) and also available from the University of Minnesota Human Rights Library. The documents contained in the Annual Report are on Westlaw International Materials from 1994 onwards, under 'Organization of American States: Inter-American Commission on Human Rights'.
Indexes to Inter-American Commission cases have appeared in the American University Journal of International Law and Policy (10 Am.U.J.Int'l L.& Pol'y 19) and the American University International Law Review (16 Am. U. Int'l L. Rev. 353). Both journals are held at IALS and are also on HeinOnline.
For more information about inter-American human rights, see Naddeo and Avalos, 'The Inter-American System of Human Rights: A Research Guide' (2022), on New York University's Globalex website.
International Court of Justice (ICJ, 1946 - ): the ICJ publishes its decisions and related documents in two series: Reports of Judgments, Advisory Opinions and Orders and Pleadings, Oral Arguments and Documents, both held at IALS.
All ICJ judgments, opinions, pleadings and other case documents are on the ICJ website. Westlaw International Materials, HeinOnline and Lexis+ have a comprehensive collection of ICJ judgments and opinions; Lexis also has some of the pleadings and other documents, but not all of them. Selected ICJ decisions are found in general sources such as ILR and ORIL.
International Criminal Court (ICC): the ICC website provides transcripts and other court documents; WorldLII also has ICC cases. Summaries of selected ICC decisions appear in The Annotated Digest of the International Criminal Court, edited by Cyril Laucci (Martinus Nijhoff, 2007- , held at IALS). A large collection of ICC cases is available in the International Criminal Law module of ORIL (see IALS Law Databases page), while selected cases are in ILR and ILM (outlined above).
Outlines of ongoing proceedings are included in the annual publication, Report of the International Criminal Court: Note by the Secretary-General, available on the ICC website and in the UN Official Document System.
The ICC Legal Tools website is an extensive resource for researching international criminal law. It provides documents and decisions of the ICC, scholarly commentary and national legislation implementing the ICC Statute (it also covers other international criminal courts/tribunals, municipal cases and more). The site was developed by the Legal Advisory Section (LAS) of the Office of the Prosecutor at the International Criminal Court.
The Permanent Court of International Justice (PCIJ, operated 1922 to 1940, dissolved 1946): PCIJ decisions and related documents were published by the Court in Publications of the Permanent Court of International Justice series A, B, A/B and C, all held at IALS.
PCIJ cases are also on the ICJ website and HeinOnline, and selected ones appear in sources such as the International Law Reports and Oxford Reports on International Law.
International law cases by subject
Arbitration
The following sources cover arbitral awards in disputes between states:
ICSID Reports: Reports of Cases Decided under the Convention on the Settlement of Investment Disputes.... (Grotius, 1993 - ). Has cases dating from 1975 onwards; held at IALS; also available online - see Catalogue. There is also a database of ICSID cases on the World Bank website.
Iran-United States Claims Tribunal Reports (Grotius, 1983 - ): all the decisions of the Tribunal since it was established in 1981. Held at IALS; also on Westlaw International Materials.
Reports of International Arbitral Awards (RIAA; United Nations, c.1948 - ): arbitrations between states from the 1920s onwards. IALS has the printed series and it is also available on the UN website and HeinOnline.
Commercial arbitration is not covered by this guide, but ASIL's Electronic Resource Guide has a chapter on researching international commercial arbitration.
Criminal (see above for the International Criminal Court)
Many international / internationalised criminal tribunals provide their decisions on the internet, including the Extraordinary Chambers in the Courts of Cambodia (ECCC); the International Criminal Tribunal for Rwanda (ICTR); the International Criminal Tribunal for the former Yugoslavia (ICTY); the Special Court for Sierra Leone; and the Special Tribunal for Lebanon. Some of these tribunals have completed all their cases, but their websites are maintained as information sources.
Key decisions appear in Annotated Leading Cases of International Criminal Tribunals (Intersentia, 1999 - ), which is held at IALS. The International Criminal Law module of ORIL (see IALS Law Databases page) includes cases concerning Sierra Leone, Lebanon, Cambodia, Rwanda and Yugoslavia; it also covers the Nuremberg Tribunal, the Mechanism for International Criminal Tribunals and a few other bodies. IALS has the ICTY's print series, Judicial Reports.
The ICC Legal Tools website covers selected decisions, founding documents, regulations and other documentation relating to international and internationalised criminal tribunals and related bodies: the Bosnian War Crimes Chamber; the ECCC; the ICTY; the ICTR; the Nuremberg Tribunal; the International Military Tribunal for the Far East; the International Residual Mechanism for Criminal Tribunals; the Iraqi High Tribunal; the Special Court for Sierra Leone; the Special Panel for Serious Crimes (East Timor); the Special Tribunal for Lebanon; and the UN Mission in Kosovo.
Other sources of international criminal cases include WorldLII's International Courts and Tribunals collection, the International Law Reports and International Legal Materials.
Further information about international criminal justice is available in Mackenzie et al, Manual on international courts and tribunals (2nd edn, OUP 2010; print and e-book available - see Catalogue).
Human rights
The International Human Rights Law module of Oxford Reports on International Law has decisions from all the major human rights bodies, including UN committees. Further information about human rights cases is available above.
Maritime
The International Tribunal for the Law of the Sea (ITLOS) provides all its cases on its website and also publishes them in Reports of judgments, advisory opinions, and orders (IALS Library's holdings are incomplete). ITLOS cases are included in the International Courts of General Jurisdiction module of Oxford Reports on International Law (ORIL, via IALS Law Databases page). Selected cases have been reported in ILR.
Trade
World Trade Organization decisions are available on the WTO website and in the printed series Dispute Settlement Reports (held at IALS). They are also on the subscription databases Lexis+, Westlaw International and TradeLawGuide (all available via IALS Law Databases page); commentary on WTO decisions is available on TradeLawGuide.
The teachings of leading publicists - experts in international law - may be cited as evidence of the rules of international law (ICJ Statute art.38(d)). These teachings may be found in books, journals, encyclopedias, the publications of the International Law Commission and elsewhere; they are even available in video format, in the UN Lecture Series.
In the UK, established general works on international law include Robert Jennings, Oppenheim's International Law (9th edn., OUP 1992) and James Crawford, Brownlie's Principles of Public International Law (9th edn, OUP 2019).
The Max Planck Encyclopedia of Public International Law has commentary by leading authorities, arranged by topic.
The UN provides a free collection of scholarly writings online via its Research Library, under an arrangement with HeinOnline.
Further information about books, journals and the Max Planck Encyclopedia is given below.
IALS has a very large collection of books on public international law, both printed and online: see Library Catalogue.
The e-book collections most relevant to international law research include Brill Online's International Law collection, Elgar Online's International Economic Law and Public International Law collections, Oxford Scholarly Authorities on International Law, Cambridge Core and Oxford Scholarship Online (see IALS Law Databases page). Many old treatises on international law are available in HeinOnline's Legal Classics library (see Law Databases page) and/or the free Hathi Trust Digital Library.
The main location for printed books on public international law is at classmarks starting 'SG', on the third floor, but some key texts are in the Short Loan Collection. Many older works are kept in the Depository, but they can be brought out on request (please ask at the Enquiry Desk by the library entrance).
The following are a small selection of standard treatises, critical works, research handbooks and research reviews held at IALS:
Standard works
Critical / regional approaches
Handbooks and research reviews
IALS Library has a substantial collection of international law journals and yearbooks, in hard copy and/or online: see Library Catalogue. (Yearbooks are annual publications containing commentary, international law updates and state practice information, typically.)
The following titles are a small selection of the available titles:
African Yearbook of International Law (AYIL), African Association of International Law / Brill, 1993 -
American Journal of International Law (AJIL), American Society of International Law, 1907 -
Asian Yearbook of International Law (AsYIL), Foundation for the Development of International Law in Asia / Brill, 1991 - (open access)
British Year Book of International Law (BYBIL), OUP, 1920 -
International and Comparative Law Quarterly (ICLQ), British Institute of International and Comparative Law / Cambridge University Press,1952 -
International Community Law Review (Int CL Rev), Brill, 2006- ; formed by merger of International Law Forum (1999-2005) and Non-State Actors and International Law (2001-2005)
Journal du droit international, formerly Journal du droit international privé et de la jurisprudence comparée (cited by the name of its founder, Clunet), various publishers, 1874 - ; historical issues free online (1874-1914)
Recueil des cours / Collected Courses, Hague Academy of International Law, 1923 -
Third World Approaches to International Law Review / TWAIL Review, University of Windsor, Faculty of Law, 2020- (open access)
Zeitschrift für ausländisches öffentliches Recht und Völkerrecht / Heidelberg Journal of International Law, (ZaoRV / HJIL): Max Planck Institute for Comparative Public Law and International Law, 1929 - (archive at https://www.zaoerv.de/, recent volumes on open access from Nomos e-library)
To do a wide-ranging literature search for articles on international law topics, use HeinOnline, Westlaw (UK and International), Index to Foreign Legal Periodicals (covers international as well as foreign law), Collected Courses of the Hague Academy of International Law and Lexis+. See the IALS Databases guide for more information.
Some key free online resources are listed below. Links to many other websites are given in each section of this guide, above.
Audiovisual Library of International Law: the UN's free international law library, with videoed lectures, scholarly writings, treaties, cases, research guides and other material.
International Law Commission (ILC): this UN body develops and codifies international law; its website provides ILC publications from 1949 onwards, and a research guide.
Opinio Juris: blog devoted to international law and international relations, founded by legal scholars Chris Borgen, Peggy McGuinness and Julian Ku and run in partnership with the International Commission of Jurists.
Public International Law: A Beginner's Guide: a Library of Congress research guide by Louis Myers.
UN Treaty Collection: free access to the UN Treaty Series, League of Nations Treaty Series and related information.
United Nations Documents: gateway to the documentation of the UN General Assembly, Security Council, Secretariat and other UN bodies, including links to the Official Document System and the UN Digital Library. (See also the IALS UN Research Guide.)
WorldLII International Law Library: free collection of treaties, international court decisions, journals, yearbooks and other international law material.