A great place to start - Dictionaries and Encyclopaedias
These reference materials link to significant primary and secondary sources for a range of international law topics, and provide definitions to key legal terms.
The Max Planck Encyclopedia of Public International Law (MPEPIL) is a comprehensive online resource containing over 1600 peer-reviewed articles on every aspect of public international law.
(UniMelb staff & student access) provides concise and authoritative scholarly commentary and bibliographical guidance on many international law topics, arranged alphabetically.
Combines terminology and pertinent descriptive information on essentials of international law, including legal terms, prominent decisions, incidents, judicial and literary figures, treaties and conventions and organisations and institutions. References for further research includes cases, treaties, journal articles, and websites. Alphabetically arranged.
(via Hein Online) Online database that directs researchers to sources, including encyclopaedias, that compare multiple jurisdictions on focused subjects. Includes international law resources.