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Contemporary international lawmaking is characterized by a rapid growth of “soft law” instruments. Interdisciplinary studies have followed suit, purporting to frame the key question states face as a choice between soft and “hard” law. But this literature focuses on only one form of hard law—treaties—and cooperation through formal institutions. Customary international law (CIL) is barely mentioned. Other scholars dismiss CIL as increasingly irrelevant or even obsolete. Entirely missing from these debates is any consideration of whether and when states might prefer custom over treaties or soft law.

Library of Congress Subject Headings

Customary international law, International law, Treaties, Rational choice theory