This paper reviews fundamental concepts in environmental economics and explores theoretical results regarding the choice of the key policy instruments for the control of externalities: taxes, subsidies and marketable permits. The paper explains why today market mechanisms are increasingly being used as a tool for allocating unpriced rights and scarce resources. We survey how significant market imperfections, a pre-existing regulatory environment and concentration in both permit and output markets can impede the proper functioning of a permit system. The main factors that affect the effectiveness of marketable permits are then discussed. Given the importance of understanding the emission permit price formation, we overview recent attempts at...