Treaties (also called covenants, protocols, acquis, conventions, pacts or charters) are international agreements between states and/or international organizations. Treaties are primary sources of international law.
Conventional international law is based on consent of state parties and as such treaties applies only between those consenting parties. In determining treaty application,
Treaties only bind nonparties when they form the basis for customary international law. Customary International Law is formed when states consistently act in a certain way (state practice) out of a sense of legal obligation (opinio juris). Evidence of state practice includes domestic legislation, regulations, treaties, judicial decisions, diplomatic communications, NGO and IGO practice (for example General Assembly Resolutions and state voting practice). Look at judicial decisions and executive communications for evidence of opinio juris. A state may escape the application of customary international law by being a persistent objector.
Find Secondary Sources Explaining how to Interpret Treaty Law
If there is an official website for the treaty, as there are with many major treaties, this information is usually found on that website. Otherwise, you can check a Treaty Index, or a database containing the full-text of the treaty.
Which source you will find most useful for locating the treaty text depends on what information you have about the treaty:
For help understanding the Vienna Convention on the Law of Treaties, here is an Introductory note.
If you prefer to watch videos to learn more, explore the Lecture Series on this website.
Commentary on the 1969 Vienna Convention on the Law of Treaties by 
The Oxford Guide to Treaties by 
Modern Treaty Law and Practice by 
The Life and Death of International Treaties by 
Treaty Interpretation by Depending on which nation states are parties to the treaty, there are different sources that provide information on the status of the treaty.
A Treaty Index is a tool for finding treaties based on the involved parties, subject matter, dates of entry into force, or other related characteristics.
If the U.S. is a party to the treaty you can use these finding tool to get more information about the treaty, including some status information and citation(s) to the treaty that you can use in HeinOnline to pull up the full text.
In addition to these searchable full-text U.S. treaty sources within Lexis and Westlaw there are also topic specific sources.
For Treaties between the U.S. and Tribal Governments, see:
Some subscription databases and websites provide access to treaties on a specific topic.
The mission of the Council of Europe is to promote democracy, human rights and the rule of law across Europe and beyond. To that end, they maintain a website that provides access to their treaties related to these topics.
If you know the year that a treaty to which the U.S. is a party, came into force (information that you can get from the Treaties in Force document referenced above), you can use these U.S. Government official sources to find the full text of the treaty:
Major Treaties used to found International Bodies, usually have their own websites, with the treaty text as well as status information and sometimes also domestic implementing legislation. A few examples are provided below, but this is not an exhaustive list. You can do a Web search for the International Body and then browse the website to looks for the founding documents or if you know the name of the treaty , you can do a Web search to see if there is an official website for the treaty.
There is no one database for the kinds of domestic legislation that implements treaty law. However, International bodies sometimes maintain a database of domestic laws implementing treaty law on specific topics.
The ICRC is an example of an organization that maintains a database of select legislation and case law implementing IHL treaties and other related international instruments.
In the same way that you would use legislative history to interpret an ambiguous statute, you can consult Travaux préparatoires to interpret an ambiguous treaty.
Sources of Travaux préparatoires include UN Materials documenting the treaty negotiation process. For some specific treaties, there may be online or print collections of Travaux préparatoires. You can do a web search to find online collections, although a few examples are provided below. For print collections, you can search the UC Law SF catalog, or WorldCat. Some sample searches as well as examples of travaux préparatoires in our collection for specific treaties are provided below.
For journal articles and books on specific treaties, please use these resources:
All U.S. treaties, whether currently in-force, expired, or not-yet officially published. Includes such prominent collections as the United States Treaties and Other International Agreements set, as well as famous sets from Bevans, Miller, Malloy and others.
Contains more than 2,500 law and law-related periodicals. Coverage for all journals is from inception and goes through the most currently published issues allowed based on contracts with publishers. Search by article title, author, subject, state or country published, full text, and narrow by date.