The U.S. State Department's Office of Treaty Affairs is an essential resource for U.S. treaty research.
Since 1945, the State Department has assigned individual TIAS numbers to U.S. treaties and agreements. From 1950 to 1984, these were collected into bound volumes, U.S. Treaties and Other International Agreements (UST, available via Hein Online and in print). Following that, treaties were published as separate pamphlets (or slips) and distributed in paper form. The Treaty Affairs Office web site provides access to Texts of International Agreements to which the US Is a Party (TIAS) back to the mid-1990s, and selectively prior to that. This site also provides guidance on Finding Agreements; Treaties Pending in the Senate (having not received Senate consent to ratification); and Treaty Actions, an archived record of actions taken by states in regard to international agreements (to 2008).
Hein Online's U.S. Treaties and Agreements Library provides access to TIAS Agreements back to 1982, along with most other official and unofficial sources for U.S. treaties and agreements.
There is a considerable backlog of treaties and agreements that have been entered into but have not been published in the TIAS series. For such agreements, consult Kavass's Current Treaty Index (1982-2021) on Hein Online. In the Kavass system, treaties are assigned temporary "KAV" numbers and copied from unofficial sources. See KAV Agreements, also on Hein Online. See also the box below for information on Senate documents, which may provide the text of treaties not available in TIAS.
For the most recent treaties in reverse chronological order, see this page at the State Department website.
Before a treaty is published as a TIAS pamphlet, the text of a treaty may be available as a Senate document. Senate treaty documents include the full text of the treaty, as well as letters of transmittal from the Secretary of State and/or the President. Senate executive reports include analysis of a treaty by the Foreign Relations Committee, a recommendation as to whether the treaty should be approved by the full Senate and a statement whether approval should be made subject to one or more reservations or declarations.
Hein Online provides access to the text of Senate Treaty Documents (1980-2015, arranged numerically). Governmental sources for treaty documents are listed below.