In ordinary English usage, denunciation, from to denounce is essentially an accusation of wrongdoing.
In the context of a treaty, denunciation or abrogation is the announcement of its termination. Some treaties contain a termination clause that specifies that the treaty will terminate if a certain number of nations denounce the treaty. For instance, the Single Convention on Narcotic Drugs' Article 41 specifies that the treaty will terminate if, as a result of denunciations, the number of Parties falls below 40.
Treaties without termination clauses 
Article 42 of The Vienna Convention on the Law of Treaties states that "termination of a treaty, its denunciation or the withdrawal of a party, may take place only as a result of the application of the provisions of the treaty or of the present Convention". Article 56 states that if a treaty does not provide for denunciation, withdrawal, or termination, it is not subject to denunciation or withdrawal unless:
- it is established that the parties intended to admit the possibility of denunciation or withdrawal; or
- a right of denunciation or withdrawal may be implied by the nature of the treaty.
Any withdrawal under Article 56 requires 12 months' notice.
The Vienna Convention does not apply to all nations; the United States, for instance, is not a Party. This makes it unclear exactly how much notice the U.S. must give when withdrawing from treaties lacking a termination clause. For example, on March 7, 2005, the U.S. announced that it was withdrawing from the Consular Convention’s Optional Protocol Concerning the Compulsory Settlement of Disputes, a treaty that lacks a termination clause.
- Frederic L. Kirgis (March 2005). "ASIL Insights". The American Society of International Law. The American Society of International Law. Retrieved 21 May 2012.
- Kirgis, Frederic L.: Addendum to ASIL Insight, President Bush’s Determination Regarding Mexican Nationals and Consular Convention Rights, ASIL Insight, Mar. 2005.
- Single Convention on Narcotic Drugs, International Narcotics Control Board.
- Vienna Convention on the Law of Treaties, International Law Commission.