This term typically refers to a collection of records relating to a negotiation of a treaty. These records can take the form of
They can be valuable research material not only for scholars but also for lawyers and courts interpreting the meaning of treaty provisions.
The following is an introduction to these materials:
Documents without Borders by Cyril Robert Emery. Published in the fall of 2012 in Documents to the People, v.40, no.3, p. 12-13.
United Nations Photo: Genocide Convention Draft, June 1947
If published, Travaux Préparatoires are usually available in a UN depository library (e.g., UHM's Hamilton Library). They may also be found on official UN sites for the treaty, which may require searching in the general records of the organization involved in drafting and negotiating the treaty. There might even be records published for a specific treaty. Some examples:
The UN Audiovisual Library of International Law offers information on UN treaties from a multimedia perspective. The Historic Archives pages will contain legal instruments, each with a brief introduction prepared by a law scholar or practitioner, its procedural history and related documents, and any accompanying audiovisual materials.