I started writing this book many years ago. All these years I have been thinking about the distinct area (an intersection of political science and constitutional law) that is composed of the amendment rules (the articles of the constitution) and their consequences (the constitutional amendments). What makes them distinct is that in the overwhelming majority of countries there is a difference between the amendment rules and the rules of any other legislation.

The first article of the project,Footnote ¹ coauthored with Dominic Nardi, focused on OECD countries under the assumptions that the relations uncovered in this set would be more stable and the data would be more readily available. Both assumptions were true, and the only dataset that included our independent variable (constitutional rigidity) was aggregating a series of indexes including the amendment frequency.

I realized that I had to expand the dataset to include democracies and change my independent variable (constitutional rigidity) so it would be derived only from the amendment provisions of the corresponding constitution. I got the idea from my book Veto Players to use two different approximations: the number of veto players and the qualified majority required for decisions. An article materialized,Footnote ² and the previous results were corroborated for the whole set of democracies with both constitutional rigidity indicators. This is the basis for Chapter 7 of this book after reworking the variables according to later research results. I knew that I needed to combine these two independent variables, but I left that for the next article along with better measurements of amendments.

The next attempt took several years,Footnote ³ wherein I evaluated the significance of amendments in the more than 100 democratic countries, created the composite measure of constitutional rigidity (presented now in Chapter 2), and used the appropriate statistical method for analysis of the data, which is based not only on the estimation of the effect of the independent variable but also on its variance. This is now presented in Chapter 6. During this long period of gestation of the argument, the idea of this book was beginning to emerge, reinforced by side events revolving around specific countries.

First, the senate of Italy in 2016 invited me to talk about the consequences of the upcoming constitutional revision which would reduce its powers; indeed, the amendment would abolish the famous “symmetric bicameralism” where the two chambers have identical powers to the extent that the constitution does not differentiate between the two, using the expressions “either chamber” or “both chambers.” My talk was later published in a professional article,Footnote ⁴ and now parts of it are included in Chapter 4.

Second, I was invited by the Inter-American Development Bank and the government of Chile to a conference on constitutional reform in Chile (Santiago 2016), and my talk became an article in a professional journal,Footnote ⁵ which generated a discussion with two Chilean constitutional experts.Footnote ⁶ Parts of these articles and debates are also included in Chapter 4.

In the meantime, the results of my empirical analysis of the frequency of constitutional amendments had materialized, and the exceptional position of Mexico on the plot of countries demanded an explanation. How was it possible for a country with high constitutional rigidity (according to my indicators) to have so many amendments? The answer is provided in the article coauthored with Edwin Atilano-Robles.Footnote ⁷ I thank him for permitting me to include it in this book as Chapter 5.

There are some additional chapters in the book which were created in order to complete the picture. Chapter 1 shows the diversification of amendment institutions throughout the world. Chapter 3 puts together the different cultural approaches that are presented either as competitive or complementary to the institutional perspective presented in this book. Finally, Chapter 8 expands the work I had started some twenty years ago about the courts and the role of judges, but now with a focus on constitutional and supreme courts making decisions on constitutional issues. I was arguing then that the discretion of courts increases with the size of the legislative core because of how difficult it is for the political system to make decisions overruling them. The same argument is presented in this book about the decisions of constitutional or supreme courts, but the yardstick of difficulty this time is the amendment of the constitution. The results corroborate the expectations, but, as I argue, they are weak because the dataset is very small.

During this long journey I had many supporters and co-travelers for at least part of the way. A big part of the work was done while I was a visiting fellow at the Kellogg Institute. I would like to thank the Kellogg Institute and the University of Michigan for financial support. I would also like to thank the following colleagues that provided amendment significance ratings: Şener Aktürk, Eduardo Alemán, Rod Alence, Abel Djassi Amado, Ana Catalina Arango Restrepo, Jorge Baquerizo, Kamila Bezubik, Agnieszka Bień-Kacała, Eszter Bodnár, Catarina Santos Botelho, Mario Cajas, Cláudio Gonçalves Couto, Jesse Crosson, Javier Duque Daza, Boniface Dulani, Arolda Elbasani, Alan Fenna, Martina Flick, Claudio Fuentes, Venelin I. Ganev, Aris Georgopoulos, Marco Giuliani, Magnus Hagevi, Gábor Halmai, Allen Hicken, Giuseppe Ieraci, Christian Jensen, Aida Just, Yannis Karagiannis, Dean Knight, Thomas Koelble, Viktoriia Kolesnyk, Amie Kreppel, Ming-Sung Kuo, Nikolas Kyriakou, Tomáš Ľalík, Mahendra Lawoti, Sokol Lleshi, Małgorzata Lorencka, Emmett Macfarlane, Lára Magnúsardóttir, Robert Mattes, Mikko Mattila, Milan J. N. Meetarbhan, Wojtek Mojski, Woojin Moon, Juan Andres Moraes, Erika Moreno, Wolfgang Claudius Müller, Malkhaz Nakashidze, Noah Nathan, Gabriel Negretto, Joakim Nergelius, Bertil Emrah Oder, Eoin O’Malley, Reijer Passchier, Darko Pavlovski, Bjørn Erik Rasch, Julio Ríos-Figueroa, Tatiana Rizova, Juan Carlos Rodríguez-Cordero, Matt Ryan, Anna Rytel-Warzocha, Camilo Emiliano Saavedra Herrera, Sebastian Saiegh, Pascal Sciarini, Aqil Shah, Ulrich Sieberer, Güneş Murat Tezcür, Brian Turner, Wilson Tay Tze Vern, Arta Vorpsi, Jarle Weigård, Oya Yeğen, and Francesco Zucchini. I would also like to thank Nikos Alivizatos, Yannis Anastassakos, Rogerio Arantes, Paolo Carozza, Eric Chang, Michael Coppedge, Barbara Koremenos, Scott Mainwaring, Iain McLean, Kevin Quinn, Bjorn-Eric Rasch, Julio Ríos-Figueroa, Kaare Strom, and Vassilis Tzevelekos for critical comments; Tom Ginsburg for providing me with the data on amendments; and Richard Albert for providing me with the means to collect data on the significance of amendments through the blog site ICONnect. I am also indebted to Mitch Bosley, Jesse Crosson, Pedro Luz de Castro, Anna Halstenbach, Joe Klaver, Julia Maynard, Li-Hong Weng, and Hyeon Young Ro for excellent research assistance.