This publication includes three case studies that address what happened in Bolivia, Costa Rica and the Ecuador, which aims to rebuild the process it resulted in the adoption of such rules and answer, from each context national, to a series of questions. Among these, how the debate over party arose and evolved, what was the role of the different social and political actors, which lobbying strategy was used, and what were the determining factors to achieve its approval. Also, what were the arguments put forward by those who opposed. This publication also includes an introductory chapter which aims to place the debate on Latin America within a broader global context. For this reason, it analyzes how concept of parity emerged in Europe, what should be understood by this concept and what are their conceptual differences with respect to affirmative action. It develops also, briefly, the process of approval, implementation and impact of the parity in a number of countries that have adopted it out of the Latin American context, with the aim of extracting some lessons learned that can serve as a guide in this region.