Constitutional reform (1999-2001) delegated to Regions new legislative and administrative powers and designed a form of government based on the distinction of roles between Regional Cabinet responsible of government and Regional Council responsible of control role and oversight on policymaking. Reforms lead Regional Councils to act as decisional parliament structuring their support administrations as consulting staff and designing mechanisms of governance of support staff based on the interdependence between politicians and administrators. Rhetoric of public sector reform and institutional pressures lead to organizational choices about design and governance of administrative structure. Mechanisms of governance drawn by legislative framework and organizational design of parliamentary administrations coherently with different models of parliament and administration may shape the relationship between politicians and administrators along a continuum redesign of boundaries between separation, overlapping and complementarity of roles.