Treaties are international agreements between nations. Sometimes called conventions, declarations, accords, protocols, etc, they constitute the bulk of public international law research. Treaties can be bilateral, meaning that they apply only to two countries, or multilateral, meaning that several countries have bound themselves in an agreement.
The general strategy for finding treaties is two-fold. Begin with a finding aid, which will give you a citation; then, go to a treaty collection for an actual copy of the treaty. Below is a short list of common sources for treaties.
Treaties in Force
This annual publication indexes bilateral and multilateral treaties currently in force as of January of the current year. It gives citations to all major treaty publications as well as links to online depositories when available. At the beginning of the volume there is a table explaining what the abbreviations stand for so that you can locate the treaty in a collection. You can keep track of treaties being considered in the current session of Congress through the US Senate's webpage on treaties.
United States Treaty Index: 1776-1990 and Current Treaty Index
If a treaty is no longer in force, check the United States Treaty Index: 1776-1990 and its update, Current Treaty Index. These volumes index treaties, regardless of whether in force, by treaty number, chronology, country, and subject.
Treaties and Other International Act Series (TIAS)
Official Source for all US Treaties and Agreements after 1950
U.S. Treaties and Other International Agreements (UST)
Annual official compilation of the TIAS
United States Statutes at Large (Stat.)
Official source for pre-1950 treaties.
Bevans -- Treaties and Other International Agreements of the United States of America
Compilation of treaties from 1776-1949.
Unperfected Treaties of the United States of America
Compilation of treaties that were signed but not ratified by the US between 1776-1976.
For treaties to which the United States is not a party, check one of the following sources:
United Nations Treaty Series (UNTS)
This source contains treaties entered into by UN members since that organization was officially formed on Oct. 24, 1945.
League of Nations Treaty Series (LNTS)
This source contains treaties entered into by League of Nations members from 1920-1946.
Consolidated Treaty Series (CTS)
This source contains treaties from around the world from 1648-1919. It comes with a finding aid called Index-Guide to Treaties: Based on the Consolidated Treaty Series, which lists treaties by date and country.