There has not been a constitutional convention since the original in Philadelphia. A 2016 report from the Congressional Research Service discusses the process of calling a convention, as well as the questions and uncertainties surrounding that process. There have been 27 amendments, but passing one is very hard.
In Pew Research Center surveys, Americans overwhelmingly favor several proposed changes to the U.S. political system, from term and age limits for government officials to campaign finance limitations. But many of those changes would require amending the Constitution, which is extremely difficult. The Constitution has been in effect for 237 years but has been formally amended just 27 times.
Using a classification scheme developed by the late political scientist Donald S. Lutz, we scored the amendment rules of 101 democratic constitutions. (The other five democracies have “uncodified” constitutions, meaning their governance rules are distributed across multiple statutes, legal precedents, customs and unwritten norms.) For constitutions that contain more than one amendment procedure, we used the “least difficult” path, which may or may not be the most frequently employed.
Of all 101 constitutions, the U.S. Constitution has the second-most onerous amendment process. Amendments must be approved by two-thirds votes in both the House and Senate – itself a tall order in these polarized times – and then be ratified by three-quarters of state legislatures, or 38 of 50.
The only democracy whose constitution is even harder to change is the Federated States of Micronesia (FSM), a former U.S. trust territory in the South Pacific with about 76,000 inhabitants. The easiest path to changing the FSM’s constitution involves two separate two-thirds majority votes in the 14-person legislature, approval by the country’s president, and subsequent approval by three-quarters of voters in at least three of the FSM’s four states.
Other countries with constitutions that are nearly as hard to change are Palau, Switzerland and Australia. Like the U.S. and the FSM, these countries all require ratification at both the national and state levels.
At the other extreme, many countries with unicameral (single-chamber) legislatures can amend their constitutions much like how they pass regular laws, just requiring a larger majority in favor.
Difficulty score based on easiest pathway, as specified in constitution

Note: When a constitution specifies more than one amendment process, the “difficulty of amendment” scores represent the least difficult process. Data is based on the 106 countries we classify as democracies and includes some fully self-governing territories whose sovereign status is disputed.
Source: Pew Research Center analysis using scoring system based on “Toward a Theory of Constitutional Amendment” by Donald S. Lutz (American Political Science Review, June 1994).


