The rule of the shorter term, also called the comparison of terms, is a provision in international copyright treaties. The provision allows that signatory countries can limit the duration of copyright they grant to foreign works under national treatment to no more than the copyright term granted in the country of origin of the work.

International copyright treaties such as the Berne Convention (BC) or the Universal Copyright Convention (UCC) work through national treatment: signatory countries agree to grant copyright to foreign works under their local laws and by the same rules they grant copyright to domestic works. Whether a work is eligible to copyright, and if so, for how long that copyright exists, is governed by the laws of the country where copyright on the work is claimed.^[1] The Berne Convention and also the UCC define only the minimum requirements for copyrights that all signatory countries must meet, but any country is free to go beyond this minimal common denominator in its legislation. This is most noticeable in the duration for which copyrights are upheld. The Berne Convention lays down a minimal general copyright term of 50 years beyond the death of an author (50 years p.m.a.).^[2] But many countries have a longer term, such as 70 years p.m.a., or even 100 years p.m.a..

One and the same work may thus be copyrighted for different times in different countries (since, per lex loci protectionis, the copyright rules of each country apply within its jurisdiction, regardless of the work's country of origin). Its copyright may have expired already in countries with a minimum term, but at the same time, it may still be copyrighted in other countries that have longer copyright terms.^[1] National treatment may thus lead to an imbalance: works originating from countries with minimal copyright terms are copyrighted longer in other countries that have longer copyright terms. In that situation, works from a country that goes beyond the minimum requirements of a treaty may already have entered the public domain in foreign countries with shorter copyright term while still being copyrighted at home.

In such cases, the rule of the shorter term makes allowance for reciprocity in exception to the normal national treatment. Countries with a long copyright term may apply only the shorter foreign term to works from countries that have such a shorter term.

In the Universal Copyright Convention, the comparison of terms is spelled out in article IV(4)(a), which reads:

No Contracting State shall be obliged to grant protection to a work for a period longer than that fixed for the class of works to which the work in question belongs, in the case of unpublished works by the law of the Contracting State of which the author is a national, and in the case of published works by the law of the Contracting State in which the work has been first published. — UCC, article IV(4)(a).^[3]

Addressing concerns of the Japanese delegation, the conference chair clarified that this subsumed the case of classes of works that were not copyrightable at all in their country of origin (as specified), as these would have a copyright term equal to zero. Thus other countries would not be obliged to grant copyright on such foreign works, even if similar domestic works were granted copyright.^[4]

The application of article IV(4)(a) is not mandatory: "not being obliged to" is not equivalent to "being obliged not to".

In the Berne Convention for the Protection of Literary and Artistic Works, a similar rule exists, but not for "classes of works" but considering individual works. Article 7(8) of the Berne Convention reads:

In any case, the term shall be governed by the legislation of the country where protection is claimed; however, unless the legislation of that country otherwise provides, the term shall not exceed the term fixed in the country of origin of the work. — Berne Convention, article 7(8).^[5]

Again, application of this rule is not mandatory.^[6] Any country may "provide otherwise" in its legislation. To do so, it is not necessary to include an explicit exception in the domestic copyright law,^[7] as the example of the United States shows.

The Berne Convention also states in article 5(2) that the enjoyment and exercise of copyright

... shall be independent of the existence of protection in the country of origin of the work. Consequently, apart from the provisions of this Convention, the extent of protection, as well as the means of redress afforded to the author to protect his rights, shall be governed exclusively by the laws of the country where protection is claimed. — Berne Convention, article 5(2).^[1]

This specifies national treatment, and also makes the existence of copyright on a work in one country independent from the existence of copyright on the work in other countries (lex loci protectionis).

A WIPO study in 2011 recommended that «The difficulty of the rule of the comparison of terms applicable to the duration for protection, as provided by Article 7(8) of the Berne Convention, should at least be assessed».^[8]

The terms of existing or new bilateral treaties may moreover override these conventions, as long as such bilateral treaties meet the minimum requirements of the conventions. This is defined in article 20 of the Berne Convention^[9] and in articles XVIII and XIX of the UCC.^[10]

When the United States joined the Berne Convention, Congress explicitly declared that the treaty was not self-executing in the United States in the Berne Convention Implementation Act of 1988, section 2 (BCIA, Pub. L. 100-568).^[72] The BCIA made clear that within the U.S., only U.S. copyright law applied, and that U.S. copyright law, as amended by the BCIA, implemented the requirements of the Berne Convention (although it did not implement §18(1) of the Berne Convention, a deviation that was corrected by the Uruguay Round Agreements Act (URAA) in 1994).

This statement from public law 100-568 is repeated in the U.S. Copyright law in 17 USC 104, which assimilates foreign works to domestic works and which furthermore states in 17 USC 104(c) that

No right or interest in a work eligible for protection under this title may be claimed by virtue of, or in reliance upon; the provisions of the Berne Convention, or the adherence of the United States thereto. Any rights in a work eligible for protection under this title that derive from this title, other Federal or State statutes, or the common law, shall not be expanded or reduced by virtue of, or in reliance upon, the provisions of the Berne Convention, or the adherence of the United States thereto. – 17 USC 104(c)

Any requirements from the Berne Convention thus needed to be spelled out explicitly in the U.S. Copyright law to make them effective in the United States.^[73] But Title 17 of the United States Code does not contain any article on the rule of the shorter term. The only mention of such a rule was added in 1994 with the URAA in 17 USC 104A, which automatically restored copyrights on many foreign works, unless these works had already fallen in the public domain in their country of origin on the URAA date, which is January 1, 1996 for most foreign countries. Because there is no general rule of the shorter term in U.S. Copyright law, U.S. courts have declined to apply that rule on several occasions.

In the European Union, copyrights have been harmonized amongst the member states by the EU directive 93/98/EEC on harmonising the term of copyright protection. This binding directive, which became effective on July 1, 1995, has raised the duration of copyrights throughout the union to 70 years p.m.a. It also includes in its article 7 a mandatory rule of the shorter term for works from non-EU countries. Within the EU, no comparison of terms is applied, and—as in the Berne Convention or in the UCC—existing international obligations (such as bilateral treaties) may override this rule of the shorter term. Directive 93/98/EEC was repealed and replaced by Directive 2006/116/EC of the European Parliament and of the Council of 12 December 2006 on the term of protection of copyright and certain related rights.^[79]

Germany extends the non-applicability of the rule of the shorter term to all members of the European Economic Area in §120 of its Urheberrechtsgesetz.^[80] It also does not apply the comparison of terms to U.S. works. In a case decided on October 7, 2003 by the Oberlandesgericht of Hesse in Frankfurt am Main, the court ruled that a U.S. work that had fallen in the public domain in the U.S. was still copyrighted in Germany. The court considered the rule of the shorter term inapplicable because of the bilateral copyright treaty between Germany and the United States, which had become effective on January 15, 1892 and which was still in effect.^[32] That treaty did not contain a rule of the shorter term, but just stated that works of either country were copyrighted in the other country by the other country's laws.^[78]

The EU member states implemented Directive 93/98/EEC^[81] and Directive 2006/116/EC^[82] in their national law; however, it is not guaranteed that such national implementations are either "comprehensive or in conformity" with the Directives.