Recent literature on bureaucratic structure has gone further than studying discretions given to bureaucrats in policy making, and much attention is now paid to understanding how bureaucratic agencies are managed. This article proposes that the way in which executive governments manage their agencies varies according to their constitutional setting and that this relationship is driven by considerations of the executive's governing legitimacy. Inspired by Charles Tilly (1984), the authors compare patterns of agency governance in Hong Kong and Ireland, in particular, configurations of assigned decision-making autonomies and control mechanisms. This comparison shows that in governing their agencies, the elected government of Ireland's parliamentary democracy pays more attention to input (i.e., democratic) legitimacy, while the executive government of Hong Kong's administrative state favors output (i.e., performance) legitimacy. These different forms of autonomy and control mechanism reflect different constitutional models of how political executives acquire and sustain their governing legitimacy.