This volume focuses on the status, functions, and role of the political opposition in the frame of government of some Central and Eastern European countries. The rules and practices reinforcing the democratic decision-making process, or the ones that risk to jeopardise political pluralism by denying the opposition’s rights, are key aspects to measure the quality level of a democratic Parliament. As these are issues at the core of constitutional democracies, a number of guarantees for the opposition should be provided directly in constitutions, parliamentary rules of procedure, or other sources of law. The essays included in this volume make legal scholars and political scientists reflect on the importance of status and role of political and parliamentary opposition to better understand the dynamics affecting transition to democracy, democratic consolidation and the guarantees for pluralism, both considering the good results and the democratic backslidings occurred in some countries of this geographical area. The volume is one of the outcomes of the research activities carried out within the project “El Estatus jurídico-político de la oposición política en las Democracias representativas”, PI prof. Manuel Fondevila Marón - University of Lleida, funded by the Ministerio de ciencia e innovación of Spain (PID2020-117154GA-I00; MCIN/AEI/10.13039/501100011033), and within the project “The legal status of political opposition in the Western Balkans: a comparative analysis”, PI prof. Serena Baldin, funded by the University of Trieste.