An entrenched clause of a constitution is a provision which makes certain amendments either more difficult than others or impossible. It may require some form of supermajority, a referendum or the consent of some other party.

They are usually justified as protecting the rights of a minority from the dangers of majoritarianism, but they are often challenged by their opponents as being particularly undemocratic.

There are several examples of entrenched clauses which ultimately failed in their objectives, since their protections were undermined in unintended ways.

• The Irish Free State Constitution was required in parts to be consistent with the 1922 Anglo-Irish Treaty, including an oath of allegiance and a representative of the Crown. The checks to protect this were removed by, for example, the Irish taking control of advice to the Governor-General, and when the Senate proved obstructive its abolition.
• The initial constitution of the Union of South Africa had entrenched clauses protecting voting rights, including those of some Coloureds. They lost their votes after the Government packed the Senate and Supreme Court with its sympathisers.

Article Five of the United States Constitution contains two entrenched clauses. One clause prohibited any constitutional amendment regarding the international slave trade. This clause expired in 1808. The other clause, still in effect, states that "no State, without its Consent, shall be deprived of its equal suffrage in the Senate". This has been interpreted to require unanimous ratification of any amendment altering the composition of the United States Senate.

The unratified Corwin amendment would have amounted to another entrenched clause, protecting states' rights to continue slavery.