This subsidiary means of determining international law rules is interpreted to mean significant scholarly writing on international law, including treatises and articles. Such materials are considered "secondary sources," both in a bibliographic sense and in terms of the sources of international law.

A publicist is an international law scholar or a scholarly organization (e.g., American Law Institute). However, Article 38 of the ICJ Statute indicates that only teachings (writings) of "the most highly qualified publicists" are considered to be a source of international law. Thus, not every article or book about an international law topic would be considered a source of international law.