I. Constitutional features of parliamentary oversight in Europe -- Introduction : oversight of the executives : a European approach -- Oversight as a relational function linking parliaments to executives -- Instances of parliamentary oversight : in dialogue with other parliamentary functions -- Classifying oversight tools according to parliamentary practice -- Parliamentary oversight in bicameral systems : what role for upper houses? -- II. Instances of parliamentary oversight in sectoral policy fields -- Parliaments in international affairs : fostering democracy through the oversight of government action -- Parliamentary oversight in the EU constitutional dimension : the polycentric paradigm -- Parliamentary oversight of budget : a trade-off with budgetary decision-making?