The volume analyzes the evolution of the main elements of administrative procedures through a methodology that overcomes the traditional observation of the phenomenon only inside each legal tradition. The author studies in-depth the characteristics of the main experiences and identifies the role played by subjective legal positions in the formation of the rules on procedures. The analysis is carried out through preliminary methodological clarifications and continues with the verification of the strength with which the principles have established themselves in the national and international legal systems. In this way it has been possible to discover models of transparency and participation and identify the functions that the duty to give reasons have in the various jurisdictions. The author reconstructs the systems with which the problems of administrative inertia are tackled and resolved and the limits that the individual juridical experiences impose on the discretionary power, up to identify procedural models and their diffusion in comparative law.