If you are new to treaty research, or are unfamiliar with a particular aspect thereof, start your research with a secondary source. The introductory and in-depth resources described below provide information about treaty negotiation, ratification, entry into force, reservations, declarations, amendments, interpretation, termination, suspension, and state succession, among other topics.
Max Planck Encyclopedias of International Law Online
From the purple menu bar at the top of the homepage, click on the "Subjects" tab and select "Law of Treaties." Then search by keyword or use the filters on the left side to find articles on narrower topics within the field of treaty law.