The essay analyses the principal theories at the basis of the profound changes that took place in the 1980s and 1990s in the administrative apparatuses of the majority of the Western democracies. Theoretical interpretations are distinguished according to their analytical purposes: prescriptive (new public management doctrine), descriptive (governance theory) and explanatory (neoinstitutional analysis). Considering neoinstitutionalist theory as best suited to analysis of reform processes, the author uses its theories and methodologies to distinguish three different trajectories of administrative reform: market (United States, Australia, New Zealand, Great Britain), democratic-participative (Scandinavia and Holland) and modernization (Italy, France, Germany and Spain). Analysis of the divergences among the three trajectories is based on the interweaving of various factors: notably the characteristics of the system of government; the presence or otherwise of norms regulating the disciplining of personnel and administrative processes; the characteristics of the interests mediation system (e.g. trade-union organizations).