Evaluation – both ex post and ex ante – is part of the Rio model of governance, which emerged from the UN Earth Summit of 1992. This chapter provides a general overview of the Rio governance model that stands behind the strategic concept of Sustainable Development. This model of environmental governance has been remarkably successful as a knowledge-based model of steering – not based on power and legal obligation. However, we urgently need further improvements. The chapter therefore makes a number of suggestions as to how to strengthen the Rio model of governance. It also looks at whether evaluation should use only a top-down perspective - the implementation of Agenda 21 or of national SD strategies – or should also adopt a bottom-up perspective focusing on forces that are independent from but supportive to the strategy of SD (e.g. high energy prices or changes in WTO rules).