This paper provides an introduction to the design and use of financial and economic models that transparently quantify the impact of regulatory decisions.1 It draws on lessons from international experience in developed and developing countries in ordinary or extraordinary revisions and in the context of contract renegotiations.2 The sample of experiences to draw from is still modest and growing slowly. During the 1990s, over 200 regulatory agencies have been created in developing countries as part of infrastructure restructuring. Many are yet to adopt transparent regulatory processes. Many more fail to rely on analytical frameworks capable of addressing the most common concerns included in regulators' mandates.